diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 5776b98..d801917 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -6,7 +6,7 @@ on:
       - "v[0-9]+.[0-9]+.[0-9]+"
 
 jobs:
-  release-linux-binaries:
+  release-linux-x86_64-binaries:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source code
@@ -35,7 +35,7 @@ jobs:
             complgen-x86_64-unknown-linux-musl
 
 
-  release-arm-linux-binaries:
+  release-linux-arm-binaries:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source code
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
deleted file mode 100644
index 2a80371..0000000
--- a/.github/workflows/test.yml
+++ /dev/null
@@ -1,24 +0,0 @@
-name: Rust
-
-on:
-  push:
-    branches: [ "master" ]
-  pull_request:
-    branches: [ "master" ]
-
-env:
-  CARGO_TERM_COLOR: always
-
-jobs:
-  build:
-
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v3
-    - name: Build
-      run: cargo build
-    - name: Run tests
-      run: cargo test
-    - name: Run e2e tests
-      run: ./run-e2e-tests.bash
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a8a7701..bfef107 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
+## 0.6.0
+### Added
+
+ - Added `--regex` option for writing generated regular expression into a .dot file for debugging
+
+### Removed
+
+ - Removed `--railroad` option for diagrams generation due to limited utility
+
 ## 0.5.0
 ### Changed
 
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index b69c6cb..ae295c9 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -100,10 +100,6 @@ grep [<OPTION>]... <PATTERNS> [<FILE>]...;
 <FILE> ::= { ls };
 ```
 
-its abstract syntax tree can be visualized as a railroad diagram:
-
-![Railroad diagram](assets/railroad.svg)
-
 The DFA can be visualized as a [Graphviz diagram](https://graphviz.org/):
 
 ![DFA](assets/dfa.svg)
diff --git a/Cargo.lock b/Cargo.lock
index 865b79d..179d722 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -41,42 +41,52 @@ checksum = "c7021ce4924a3f25f802b2cccd1af585e39ea1a363a1aa2e72afe54b67a3a7a7"
 
 [[package]]
 name = "anstream"
-version = "0.2.6"
+version = "0.6.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "342258dd14006105c2b75ab1bd7543a03bdf0cfc94383303ac212a04939dff6f"
+checksum = "3ae563653d1938f79b1ab1b5e668c87c76a9930414574a6583a7b7e11a8e6192"
 dependencies = [
  "anstyle",
  "anstyle-parse",
+ "anstyle-query",
  "anstyle-wincon",
- "concolor-override",
- "concolor-query",
- "is-terminal",
+ "colorchoice",
+ "is_terminal_polyfill",
  "utf8parse",
 ]
 
 [[package]]
 name = "anstyle"
-version = "0.3.5"
+version = "1.0.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "23ea9e81bd02e310c216d080f6223c179012256e5151c41db88d12c88a1684d2"
+checksum = "862ed96ca487e809f1c8e5a8447f6ee2cf102f846893800b20cebdf541fc6bbd"
 
 [[package]]
 name = "anstyle-parse"
-version = "0.1.1"
+version = "0.2.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a7d1bb534e9efed14f3e5f44e7dd1a4f709384023a4165199a4241e18dff0116"
+checksum = "4e7644824f0aa2c7b9384579234ef10eb7efb6a0deb83f9630a49594dd9c15c2"
 dependencies = [
  "utf8parse",
 ]
 
+[[package]]
+name = "anstyle-query"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9e231f6134f61b71076a3eab506c379d4f36122f2af15a9ff04415ea4c3339e2"
+dependencies = [
+ "windows-sys 0.60.2",
+]
+
 [[package]]
 name = "anstyle-wincon"
-version = "0.2.0"
+version = "3.0.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3127af6145b149f3287bb9a0d10ad9c5692dba8c53ad48285e5bec4063834fa"
+checksum = "3e0633414522a32ffaac8ac6cc8f748e090c5717661fddeea04219e2344f5f2a"
 dependencies = [
  "anstyle",
- "windows-sys 0.45.0",
+ "once_cell_polyfill",
+ "windows-sys 0.60.2",
 ]
 
 [[package]]
@@ -153,33 +163,31 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "4.2.1"
+version = "4.4.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "046ae530c528f252094e4a77886ee1374437744b2bff1497aa898bbddbbb29b3"
+checksum = "1e578d6ec4194633722ccf9544794b71b1385c3c027efe0c55db226fc880865c"
 dependencies = [
  "clap_builder",
  "clap_derive",
- "once_cell",
 ]
 
 [[package]]
 name = "clap_builder"
-version = "4.2.1"
+version = "4.4.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "223163f58c9a40c3b0a43e1c4b50a9ce09f007ea2cb1ec258a687945b4b7929f"
+checksum = "4df4df40ec50c46000231c914968278b1eb05098cf8f1b3a518a95030e71d1c7"
 dependencies = [
  "anstream",
  "anstyle",
- "bitflags",
  "clap_lex",
  "strsim",
 ]
 
 [[package]]
 name = "clap_derive"
-version = "4.2.0"
+version = "4.4.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3f9644cd56d6b87dbe899ef8b053e331c0637664e9e21a33dfcdc36093f5c5c4"
+checksum = "cf9804afaaf59a91e75b022a30fb7229a7901f60c755489cc61c9b423b836442"
 dependencies = [
  "heck",
  "proc-macro2",
@@ -189,9 +197,15 @@ dependencies = [
 
 [[package]]
 name = "clap_lex"
-version = "0.4.1"
+version = "0.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8a2dd5a6fe8c6e3502f568a6353e5273bbb15193ad9a89e457b9970798efbea1"
+checksum = "702fc72eb24e5a1e48ce58027a675bc24edd52096d5397d4aea7c6dd9eca0bd1"
+
+[[package]]
+name = "colorchoice"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b05b61dc5112cbb17e4b6cd61790d9845d13888356391624cbe7e41efeac1e75"
 
 [[package]]
 name = "complgen"
@@ -200,57 +214,24 @@ dependencies = [
  "anyhow",
  "chic",
  "clap",
- "env_logger",
  "hashbrown 0.13.2",
  "indexmap",
  "itertools",
- "log",
  "nom",
  "nom_locate",
  "proptest",
- "railroad",
  "regex",
  "roaring",
- "slice-group-by",
- "tempfile",
  "thiserror",
  "ustr",
 ]
 
-[[package]]
-name = "concolor-override"
-version = "1.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a855d4a1978dc52fb0536a04d384c2c0c1aa273597f08b77c8c4d3b2eec6037f"
-
-[[package]]
-name = "concolor-query"
-version = "0.3.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "88d11d52c3d7ca2e6d0040212be9e4dbbcd78b6447f535b6b561f449427944cf"
-dependencies = [
- "windows-sys 0.45.0",
-]
-
 [[package]]
 name = "either"
 version = "1.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7fcaabb2fef8c910e7f4c7ce9f67a1283a1715879a7c230ca9d6d1ae31f16d91"
 
-[[package]]
-name = "env_logger"
-version = "0.10.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "85cdab6a89accf66733ad5a1693a4dcced6aeff64602b634530dd73c1f3ee9f0"
-dependencies = [
- "humantime",
- "is-terminal",
- "log",
- "regex",
- "termcolor",
-]
-
 [[package]]
 name = "equivalent"
 version = "1.0.1"
@@ -331,18 +312,6 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fed44880c466736ef9a5c5b5facefb5ed0785676d0c02d612db14e54f0d84286"
 
-[[package]]
-name = "htmlescape"
-version = "0.3.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e9025058dae765dee5070ec375f591e2ba14638c63feff74f13805a72e523163"
-
-[[package]]
-name = "humantime"
-version = "2.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9a3a5bfb195931eeb336b2a7b4d761daec841b97f947d34394601737a7bba5e4"
-
 [[package]]
 name = "indexmap"
 version = "2.7.0"
@@ -374,16 +343,10 @@ dependencies = [
 ]
 
 [[package]]
-name = "is-terminal"
-version = "0.4.6"
+name = "is_terminal_polyfill"
+version = "1.70.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "256017f749ab3117e93acb91063009e1f1bb56d03965b14c2c8df4eb02c524d8"
-dependencies = [
- "hermit-abi",
- "io-lifetimes",
- "rustix",
- "windows-sys 0.45.0",
-]
+checksum = "7943c866cc5cd64cbc25b2e01621d07fa8eb2a1a23160ee81ce38704e97b8ecf"
 
 [[package]]
 name = "itertools"
@@ -428,12 +391,6 @@ dependencies = [
  "scopeguard",
 ]
 
-[[package]]
-name = "log"
-version = "0.4.19"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b06a4cde4c0f271a446782e3eff8de789548ce57dbc8eca9292c27f4a42004b4"
-
 [[package]]
 name = "memchr"
 version = "2.6.3"
@@ -483,6 +440,12 @@ version = "1.17.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b7e5500299e16ebb147ae15a00a942af264cf3688f47923b8fc2cd5858f23ad3"
 
+[[package]]
+name = "once_cell_polyfill"
+version = "1.70.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4895175b425cb1f87721b59f0f286c2092bd4af812243672510e1ac53e2e0ad"
+
 [[package]]
 name = "parking_lot"
 version = "0.11.2"
@@ -565,16 +528,6 @@ dependencies = [
  "proc-macro2",
 ]
 
-[[package]]
-name = "railroad"
-version = "0.2.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "01fedaa01e5a17f30fbae3b16b5c28a0a396a15b74fcd9d24c11dc3d1634c823"
-dependencies = [
- "htmlescape",
- "unicode-width",
-]
-
 [[package]]
 name = "rand"
 version = "0.8.5"
@@ -716,12 +669,6 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
-[[package]]
-name = "slice-group-by"
-version = "0.3.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "826167069c09b99d56f31e9ae5c99049e932a98c9dc2dac47645b08dbbf76ba7"
-
 [[package]]
 name = "smallvec"
 version = "1.10.0"
@@ -770,15 +717,6 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
-[[package]]
-name = "termcolor"
-version = "1.2.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "be55cf8942feac5c765c2c993422806843c9a9a45d4d5c407ad6dd2ea95eb9b6"
-dependencies = [
- "winapi-util",
-]
-
 [[package]]
 name = "thiserror"
 version = "1.0.39"
@@ -811,12 +749,6 @@ version = "1.0.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e5464a87b239f13a63a501f2701565754bae92d243d4bb7eb12f6d57d2269bf4"
 
-[[package]]
-name = "unicode-width"
-version = "0.1.10"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c0edd1e5b14653f783770bce4a4dabb4a5108a5370a5f5d8cfe8710c361f6c8b"
-
 [[package]]
 name = "ustr"
 version = "0.9.0"
@@ -872,15 +804,6 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 
-[[package]]
-name = "winapi-util"
-version = "0.1.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
-dependencies = [
- "winapi",
-]
-
 [[package]]
 name = "winapi-x86_64-pc-windows-gnu"
 version = "0.4.0"
@@ -888,13 +811,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
 [[package]]
-name = "windows-sys"
-version = "0.45.0"
+name = "windows-link"
+version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "75283be5efb2831d37ea142365f009c02ec203cd29a3ebecbc093d52315b66d0"
-dependencies = [
- "windows-targets 0.42.2",
-]
+checksum = "5e6ad25900d524eaabdbbb96d20b4311e1e7ae1699af4fb28c17ae66c80d798a"
 
 [[package]]
 name = "windows-sys"
@@ -906,18 +826,12 @@ dependencies = [
 ]
 
 [[package]]
-name = "windows-targets"
-version = "0.42.2"
+name = "windows-sys"
+version = "0.60.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e5180c00cd44c9b1c88adb3693291f1cd93605ded80c250a75d472756b4d071"
+checksum = "f2f500e4d28234f72040990ec9d39e3a6b950f9f22d3dba18416c35882612bcb"
 dependencies = [
- "windows_aarch64_gnullvm 0.42.2",
- "windows_aarch64_msvc 0.42.2",
- "windows_i686_gnu 0.42.2",
- "windows_i686_msvc 0.42.2",
- "windows_x86_64_gnu 0.42.2",
- "windows_x86_64_gnullvm 0.42.2",
- "windows_x86_64_msvc 0.42.2",
+ "windows-targets 0.53.3",
 ]
 
 [[package]]
@@ -936,10 +850,21 @@ dependencies = [
 ]
 
 [[package]]
-name = "windows_aarch64_gnullvm"
-version = "0.42.2"
+name = "windows-targets"
+version = "0.53.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "597a5118570b68bc08d8d59125332c54f1ba9d9adeedeef5b99b02ba2b0698f8"
+checksum = "d5fe6031c4041849d7c496a8ded650796e7b6ecc19df1a431c1a363342e5dc91"
+dependencies = [
+ "windows-link",
+ "windows_aarch64_gnullvm 0.53.0",
+ "windows_aarch64_msvc 0.53.0",
+ "windows_i686_gnu 0.53.0",
+ "windows_i686_gnullvm",
+ "windows_i686_msvc 0.53.0",
+ "windows_x86_64_gnu 0.53.0",
+ "windows_x86_64_gnullvm 0.53.0",
+ "windows_x86_64_msvc 0.53.0",
+]
 
 [[package]]
 name = "windows_aarch64_gnullvm"
@@ -948,10 +873,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "91ae572e1b79dba883e0d315474df7305d12f569b400fcf90581b06062f7e1bc"
 
 [[package]]
-name = "windows_aarch64_msvc"
-version = "0.42.2"
+name = "windows_aarch64_gnullvm"
+version = "0.53.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e08e8864a60f06ef0d0ff4ba04124db8b0fb3be5776a5cd47641e942e58c4d43"
+checksum = "86b8d5f90ddd19cb4a147a5fa63ca848db3df085e25fee3cc10b39b6eebae764"
 
 [[package]]
 name = "windows_aarch64_msvc"
@@ -960,10 +885,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b2ef27e0d7bdfcfc7b868b317c1d32c641a6fe4629c171b8928c7b08d98d7cf3"
 
 [[package]]
-name = "windows_i686_gnu"
-version = "0.42.2"
+name = "windows_aarch64_msvc"
+version = "0.53.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c61d927d8da41da96a81f029489353e68739737d3beca43145c8afec9a31a84f"
+checksum = "c7651a1f62a11b8cbd5e0d42526e55f2c99886c77e007179efff86c2b137e66c"
 
 [[package]]
 name = "windows_i686_gnu"
@@ -972,10 +897,16 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "622a1962a7db830d6fd0a69683c80a18fda201879f0f447f065a3b7467daa241"
 
 [[package]]
-name = "windows_i686_msvc"
-version = "0.42.2"
+name = "windows_i686_gnu"
+version = "0.53.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "44d840b6ec649f480a41c8d80f9c65108b92d89345dd94027bfe06ac444d1060"
+checksum = "c1dc67659d35f387f5f6c479dc4e28f1d4bb90ddd1a5d3da2e5d97b42d6272c3"
+
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ce6ccbdedbf6d6354471319e781c0dfef054c81fbc7cf83f338a4296c0cae11"
 
 [[package]]
 name = "windows_i686_msvc"
@@ -984,10 +915,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4542c6e364ce21bf45d69fdd2a8e455fa38d316158cfd43b3ac1c5b1b19f8e00"
 
 [[package]]
-name = "windows_x86_64_gnu"
-version = "0.42.2"
+name = "windows_i686_msvc"
+version = "0.53.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8de912b8b8feb55c064867cf047dda097f92d51efad5b491dfb98f6bbb70cb36"
+checksum = "581fee95406bb13382d2f65cd4a908ca7b1e4c2f1917f143ba16efe98a589b5d"
 
 [[package]]
 name = "windows_x86_64_gnu"
@@ -996,10 +927,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ca2b8a661f7628cbd23440e50b05d705db3686f894fc9580820623656af974b1"
 
 [[package]]
-name = "windows_x86_64_gnullvm"
-version = "0.42.2"
+name = "windows_x86_64_gnu"
+version = "0.53.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "26d41b46a36d453748aedef1486d5c7a85db22e56aff34643984ea85514e94a3"
+checksum = "2e55b5ac9ea33f2fc1716d1742db15574fd6fc8dadc51caab1c16a3d3b4190ba"
 
 [[package]]
 name = "windows_x86_64_gnullvm"
@@ -1008,13 +939,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7896dbc1f41e08872e9d5e8f8baa8fdd2677f29468c4e156210174edc7f7b953"
 
 [[package]]
-name = "windows_x86_64_msvc"
-version = "0.42.2"
+name = "windows_x86_64_gnullvm"
+version = "0.53.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9aec5da331524158c6d1a4ac0ab1541149c0b9505fde06423b02f5ef0106b9f0"
+checksum = "0a6e035dd0599267ce1ee132e51c27dd29437f63325753051e71dd9e42406c57"
 
 [[package]]
 name = "windows_x86_64_msvc"
 version = "0.48.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1a515f5799fe4961cb532f983ce2b23082366b898e52ffbce459c86f67c8378a"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "271414315aff87387382ec3d271b52d7ae78726f5d44ac98b4f4030c91880486"
diff --git a/Cargo.toml b/Cargo.toml
index c7f2066..2469294 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,18 +16,13 @@ path = "src/main.rs"
 anyhow = "1.0.71"
 chic = "1.2.2"
 clap = { version = "4.2.1", features = ["derive"] }
-env_logger = "0.10.0"
 hashbrown = "0.13.2"
 indexmap = "2.7.0"
 itertools = "0.10.5"
-log = "0.4.19"
 nom = "7.1.3"
 nom_locate = "4.2.0"
-railroad = "0.2.0"
 regex = "1.9.5"
 roaring = "0.10.1"
-slice-group-by = "0.3.1"
-tempfile = "3.6.0"
 thiserror = "1.0.39"
 ustr = "0.9.0"
 
diff --git a/README.md b/README.md
index d9e93ae..32d319b 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 ## Value Proposition
 
-`complgen` generates completion scripts for bash/fish/zsh from a man-page/EBNF-like grammar.  The resulting
-standalone scripts require only the target shell to be present.  See [examples](examples/).
+`complgen` compiles man-page/EBNF-like grammars into standalone completion scripts.  See
+[examples](examples/).
 
 ## Demo
 
@@ -119,13 +119,13 @@ directory which is too specific to be generally useful.
 These nonterminals can still be defined in the grammar in the usual way (`<PATH> ::= ...`), in which case
 their predefined meaning gets overriden.
 
-### Completion descriptions (fish/zsh only)
+### Descriptions (fish/zsh only)
 
 If a literal is immediately followed with a quoted string, it's going to appear as a hint to the user at
 completion time.  E.g. the grammar:
 
 ```sh
-grep --extended-regexp "PATTERNS are extended regular expressions" | --exclude  (skip files that match GLOB)
+grep --extended-regexp "PATTERNS are extended regular expressions" | --exclude  "skip files that match GLOB";
 ```
 
 results in something like this under fish (and zsh):
@@ -160,10 +160,10 @@ cargo {{{ rustup toolchain list | cut -d' ' -f1 | grep "^$1" | sed 's/^/+/' }}};
 Note that in general, it's best to leave the filtering up to the executing shell since it may be configured to
 perform some non-standard filtering.  zsh for example is capable of expanding `/u/l/b` to `/usr/local/bin`.
 
-##### Completion descriptions
+##### Descriptions
 
 Externals commands are also assumed to produce descriptions similar to those described in the [section
-above](#descriptions-aka-completion-hints).  Their expected stdout format is a sequence of lines of the form
+above](#descriptions).  Their expected stdout format is a sequence of lines of the form
 
 ```
 COMPLETION\tDESCRIPTION
diff --git a/assets/railroad.svg b/assets/railroad.svg
deleted file mode 100644
index f3a591c..0000000
--- a/assets/railroad.svg
+++ /dev/null
@@ -1,639 +0,0 @@
-<svg class="railroad" viewBox="0 0 714 1937" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
-<style type="text/css">
-
-    svg.railroad {
-        background-color: hsl(30, 20%, 95%);
-        background-size: 15px 15px;
-        background-image: linear-gradient(to right, rgba(30, 30, 30, .05) 1px, transparent 1px),
-                          linear-gradient(to bottom, rgba(30, 30, 30, .05) 1px, transparent 1px);
-    }
-
-    svg.railroad path {
-        stroke-width: 3px;
-        stroke: black;
-        fill: transparent;
-    }
-
-    svg.railroad .debug {
-        stroke-width: 1px;
-        stroke: red;
-    }
-
-    svg.railroad text {
-        font: 14px monospace;
-        text-anchor: middle;
-    }
-
-    svg.railroad .nonterminal text {
-        font-weight: bold;
-    }
-
-    svg.railroad text.comment {
-        font: italic 12px monospace;
-    }
-
-    svg.railroad rect {
-        stroke-width: 3px;
-        stroke: black;
-        fill:hsl(-290, 70%, 90%);
-    }
-
-    svg.railroad g.labeledbox &gt; rect {
-        stroke-width: 1px;
-        stroke: grey;
-        stroke-dasharray: 5px;
-        fill:rgba(90, 90, 150, .1);
-    }</style>
-<g class="sequence">
-<path d=" M 10 24 v 20 m 10 -20 v 20 m -10 -10 h 20"/>
-<g class="sequence">
-<g class="repeat">
-<path d=" M 40 34 h 12 m 410 0 h 12 m -12 0 a 12 12 0 0 1 12 12 v 1869 m 0 -931 l -5 -5 m 10 0 l -5 5 m 0 931 a 12 12 0 0 1 -12 12 m 0 0 h -410 m 208 0 l 5 -5 m 0 10 l -5 -5 m -208 0 a 12 12 0 0 1 -12 -12 v -1869 m 0 937 l -5 5 m 10 0 l -5 -5 m 0 -937 a 12 12 0 0 1 12 -12"/>
-<g/>
-<g class="optional">
-<path d=" M 52 34 h 24 m -24 0 a 12 12 0 0 0 12 -12 v 0 a 12 12 0 0 1 12 -12 h 362 m -178 0 l -5 -5 m 0 10 l 5 -5 m 178 0 a 12 12 0 0 1 12 12 v 0 a 12 12 0 0 0 12 12 h -24"/>
-<g class="choice">
-<path d=" M 76 34 h 24 m 156 0 h 182 m -88 0 l -5 -5 m 0 10 l 5 -5 m 88 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="156" x="100" y="23"/>
-<text x="178" y="39">
---extended-regexp</text>
-</g>
-<path d=" M 76 34 a 12 12 0 0 1 12 12 v 9 m 338 0 v -9 a 12 12 0 0 1 12 -12"/>
-<path d=" M 88 55 v 33 m 338 0 v -33"/>
-<path d=" M 88 88 v 33 m 338 0 v -33"/>
-<path d=" M 88 121 v 33 m 338 0 v -33"/>
-<path d=" M 88 154 v 33 m 338 0 v -33"/>
-<path d=" M 88 187 v 33 m 338 0 v -33"/>
-<path d=" M 88 220 v 33 m 338 0 v -33"/>
-<path d=" M 88 253 v 33 m 338 0 v -33"/>
-<path d=" M 88 286 v 33 m 338 0 v -33"/>
-<path d=" M 88 319 v 33 m 338 0 v -33"/>
-<path d=" M 88 352 v 33 m 338 0 v -33"/>
-<path d=" M 88 385 v 33 m 338 0 v -33"/>
-<path d=" M 88 418 v 33 m 338 0 v -33"/>
-<path d=" M 88 451 v 33 m 338 0 v -33"/>
-<path d=" M 88 484 v 33 m 338 0 v -33"/>
-<path d=" M 88 517 v 33 m 338 0 v -33"/>
-<path d=" M 88 550 v 33 m 338 0 v -33"/>
-<path d=" M 88 583 v 33 m 338 0 v -33"/>
-<path d=" M 88 616 v 33 m 338 0 v -33"/>
-<path d=" M 88 649 v 33 m 338 0 v -33"/>
-<path d=" M 88 682 v 33 m 338 0 v -33"/>
-<path d=" M 88 715 v 33 m 338 0 v -33"/>
-<path d=" M 88 748 v 33 m 338 0 v -33"/>
-<path d=" M 88 781 v 33 m 338 0 v -33"/>
-<path d=" M 88 814 v 33 m 338 0 v -33"/>
-<path d=" M 88 847 v 99 m 0 -46 l -5 -5 m 10 0 l -5 5 m 0 46 m 338 0 v -99 m 0 52 l -5 5 m 10 0 l -5 -5 m 0 -52"/>
-<path d=" M 88 946 v 33 m 338 0 v -33"/>
-<path d=" M 88 979 v 99 m 0 -46 l -5 -5 m 10 0 l -5 5 m 0 46 m 338 0 v -99 m 0 52 l -5 5 m 10 0 l -5 -5 m 0 -52"/>
-<path d=" M 88 1078 v 66 m 0 -30 l -5 -5 m 10 0 l -5 5 m 0 30 m 338 0 v -66 m 0 36 l -5 5 m 10 0 l -5 -5 m 0 -36"/>
-<path d=" M 88 1144 v 33 m 338 0 v -33"/>
-<path d=" M 88 1177 v 33 m 338 0 v -33"/>
-<path d=" M 88 1210 v 33 m 338 0 v -33"/>
-<path d=" M 88 1243 v 33 m 338 0 v -33"/>
-<path d=" M 88 1276 v 33 m 338 0 v -33"/>
-<path d=" M 88 1309 v 33 m 338 0 v -33"/>
-<path d=" M 88 1342 v 33 m 338 0 v -33"/>
-<path d=" M 88 1375 v 33 m 338 0 v -33"/>
-<path d=" M 88 1408 v 33 m 338 0 v -33"/>
-<path d=" M 88 1441 v 33 m 338 0 v -33"/>
-<path d=" M 88 1474 v 33 m 338 0 v -33"/>
-<path d=" M 88 1507 v 33 m 338 0 v -33"/>
-<path d=" M 88 1540 v 33 m 338 0 v -33"/>
-<path d=" M 88 1573 v 33 m 338 0 v -33"/>
-<path d=" M 88 1606 v 33 m 338 0 v -33"/>
-<path d=" M 88 1639 v 33 m 338 0 v -33"/>
-<path d=" M 88 1684 v 99 m 0 -46 l -5 -5 m 10 0 l -5 5 m 0 46 m 338 0 v -99 m 0 52 l -5 5 m 10 0 l -5 -5 m 0 -52"/>
-<path d=" M 88 1795 v 99 m 0 -46 l -5 -5 m 10 0 l -5 5 m 0 46 m 338 0 v -99 m 0 52 l -5 5 m 10 0 l -5 -5 m 0 -52"/>
-<path d=" M 88 55 v 0 a 12 12 0 0 0 12 12 m 140 0 h 174 m -84 0 l -5 -5 m 0 10 l 5 -5 m 84 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="140" x="100" y="56"/>
-<text x="170" y="72">
---fixed-strings</text>
-</g>
-<path d=" M 88 88 v 0 a 12 12 0 0 0 12 12 m 132 0 h 182 m -88 0 l -5 -5 m 0 10 l 5 -5 m 88 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="132" x="100" y="89"/>
-<text x="166" y="105">
---basic-regexp</text>
-</g>
-<path d=" M 88 121 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="122"/>
-<text x="162" y="138">
---perl-regexp</text>
-</g>
-<path d=" M 88 154 v 0 a 12 12 0 0 0 12 12 m 178 0 h 136 m -65 0 l -5 -5 m 0 10 l 5 -5 m 65 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="84" x="100" y="155"/>
-<text x="142" y="171">
---regexp</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="84" x="194" y="155"/>
-<text x="236" y="171">
-PATTERNS</text>
-</g>
-<path d=" M 184 166 h 10"/>
-</g>
-<path d=" M 88 187 v 0 a 12 12 0 0 0 12 12 m 102 0 h 212 m -103 0 l -5 -5 m 0 10 l 5 -5 m 103 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="68" x="100" y="188"/>
-<text x="134" y="204">
---file</text>
-</g>
-<text class="comment" x="190" y="204">
-ls</text>
-<path d=" M 168 199 h 10"/>
-</g>
-<path d=" M 88 220 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="221"/>
-<text x="162" y="237">
---ignore-case</text>
-</g>
-<path d=" M 88 253 v 0 a 12 12 0 0 0 12 12 m 148 0 h 166 m -80 0 l -5 -5 m 0 10 l 5 -5 m 80 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="148" x="100" y="254"/>
-<text x="174" y="270">
---no-ignore-case</text>
-</g>
-<path d=" M 88 286 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="287"/>
-<text x="162" y="303">
---word-regexp</text>
-</g>
-<path d=" M 88 319 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="320"/>
-<text x="162" y="336">
---line-regexp</text>
-</g>
-<path d=" M 88 352 v 0 a 12 12 0 0 0 12 12 m 108 0 h 206 m -100 0 l -5 -5 m 0 10 l 5 -5 m 100 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="108" x="100" y="353"/>
-<text x="154" y="369">
---null-data</text>
-</g>
-<path d=" M 88 385 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="386"/>
-<text x="162" y="402">
---no-messages</text>
-</g>
-<path d=" M 88 418 v 0 a 12 12 0 0 0 12 12 m 132 0 h 182 m -88 0 l -5 -5 m 0 10 l 5 -5 m 88 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="132" x="100" y="419"/>
-<text x="166" y="435">
---invert-match</text>
-</g>
-<path d=" M 88 451 v 0 a 12 12 0 0 0 12 12 m 92 0 h 222 m -108 0 l -5 -5 m 0 10 l 5 -5 m 108 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="92" x="100" y="452"/>
-<text x="146" y="468">
---version</text>
-</g>
-<path d=" M 88 484 v 0 a 12 12 0 0 0 12 12 m 68 0 h 246 m -120 0 l -5 -5 m 0 10 l 5 -5 m 120 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="68" x="100" y="485"/>
-<text x="134" y="501">
---help</text>
-</g>
-<path d=" M 88 517 v 0 a 12 12 0 0 0 12 12 m 162 0 h 152 m -73 0 l -5 -5 m 0 10 l 5 -5 m 73 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="108" x="100" y="518"/>
-<text x="154" y="534">
---max-count</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="44" x="218" y="518"/>
-<text x="240" y="534">
-NUM</text>
-</g>
-<path d=" M 208 529 h 10"/>
-</g>
-<path d=" M 88 550 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="551"/>
-<text x="162" y="567">
---byte-offset</text>
-</g>
-<path d=" M 88 583 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="584"/>
-<text x="162" y="600">
---line-number</text>
-</g>
-<path d=" M 88 616 v 0 a 12 12 0 0 0 12 12 m 140 0 h 174 m -84 0 l -5 -5 m 0 10 l 5 -5 m 84 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="140" x="100" y="617"/>
-<text x="170" y="633">
---line-buffered</text>
-</g>
-<path d=" M 88 649 v 0 a 12 12 0 0 0 12 12 m 140 0 h 174 m -84 0 l -5 -5 m 0 10 l 5 -5 m 84 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="140" x="100" y="650"/>
-<text x="170" y="666">
---with-filename</text>
-</g>
-<path d=" M 88 682 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="683"/>
-<text x="162" y="699">
---no-filename</text>
-</g>
-<path d=" M 88 715 v 0 a 12 12 0 0 0 12 12 m 146 0 h 168 m -81 0 l -5 -5 m 0 10 l 5 -5 m 81 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="76" x="100" y="716"/>
-<text x="138" y="732">
---label</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="60" x="186" y="716"/>
-<text x="216" y="732">
-LABEL</text>
-</g>
-<path d=" M 176 727 h 10"/>
-</g>
-<path d=" M 88 748 v 0 a 12 12 0 0 0 12 12 m 140 0 h 174 m -84 0 l -5 -5 m 0 10 l 5 -5 m 84 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="140" x="100" y="749"/>
-<text x="170" y="765">
---only-matching</text>
-</g>
-<path d=" M 88 781 v 0 a 12 12 0 0 0 12 12 m 76 0 h 238 m -116 0 l -5 -5 m 0 10 l 5 -5 m 116 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="76" x="100" y="782"/>
-<text x="138" y="798">
---quiet</text>
-</g>
-<path d=" M 88 814 v 0 a 12 12 0 0 0 12 12 m 84 0 h 230 m -112 0 l -5 -5 m 0 10 l 5 -5 m 112 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="84" x="100" y="815"/>
-<text x="142" y="831">
---silent</text>
-</g>
-<path d=" M 88 847 v 0 a 12 12 0 0 0 12 12 m 314 0 h 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="132" x="100" y="848"/>
-<text x="166" y="864">
---binary-files</text>
-</g>
-<g class="choice">
-<path d=" M 242 859 h 24 m 68 0 h 80 m -37 0 l -5 -5 m 0 10 l 5 -5 m 37 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="68" x="266" y="848"/>
-<text x="300" y="864">
-binary</text>
-</g>
-<path d=" M 242 859 a 12 12 0 0 1 12 12 v 9 m 148 0 v -9 a 12 12 0 0 1 12 -12"/>
-<path d=" M 254 880 v 33 m 148 0 v -33"/>
-<path d=" M 254 880 v 0 a 12 12 0 0 0 12 12 m 52 0 h 72 m -33 0 l -5 -5 m 0 10 l 5 -5 m 33 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="52" x="266" y="881"/>
-<text x="292" y="897">
-text</text>
-</g>
-<path d=" M 254 913 v 0 a 12 12 0 0 0 12 12 m 124 0 h 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="266" y="914"/>
-<text x="328" y="930">
-without-match</text>
-</g>
-</g>
-<path d=" M 232 859 h 10"/>
-</g>
-<path d=" M 88 946 v 0 a 12 12 0 0 0 12 12 m 68 0 h 246 m -120 0 l -5 -5 m 0 10 l 5 -5 m 120 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="68" x="100" y="947"/>
-<text x="134" y="963">
---text</text>
-</g>
-<path d=" M 88 979 v 0 a 12 12 0 0 0 12 12 m 258 0 h 56 m -25 0 l -5 -5 m 0 10 l 5 -5 m 25 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="980"/>
-<text x="162" y="996">
---directories</text>
-</g>
-<g class="choice">
-<path d=" M 234 991 h 24 m 52 0 h 48"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="52" x="258" y="980"/>
-<text x="284" y="996">
-read</text>
-</g>
-<path d=" M 234 991 a 12 12 0 0 1 12 12 v 9 m 100 0 v -9 a 12 12 0 0 1 12 -12"/>
-<path d=" M 246 1012 v 33 m 100 0 v -33"/>
-<path d=" M 246 1012 v 0 a 12 12 0 0 0 12 12 m 76 0 h 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="76" x="258" y="1013"/>
-<text x="296" y="1029">
-recurse</text>
-</g>
-<path d=" M 246 1045 v 0 a 12 12 0 0 0 12 12 m 52 0 h 24 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="52" x="258" y="1046"/>
-<text x="284" y="1062">
-skip</text>
-</g>
-</g>
-<path d=" M 224 991 h 10"/>
-</g>
-<path d=" M 88 1078 v 0 a 12 12 0 0 0 12 12 m 202 0 h 112 m -53 0 l -5 -5 m 0 10 l 5 -5 m 53 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="92" x="100" y="1079"/>
-<text x="146" y="1095">
---devices</text>
-</g>
-<g class="choice">
-<path d=" M 202 1090 h 24 m 52 0 h 24"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="52" x="226" y="1079"/>
-<text x="252" y="1095">
-read</text>
-</g>
-<path d=" M 202 1090 a 12 12 0 0 1 12 12 v 9 m 76 0 v -9 a 12 12 0 0 1 12 -12"/>
-<path d=" M 214 1111 v 0 a 12 12 0 0 0 12 12 m 52 0 h 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="52" x="226" y="1112"/>
-<text x="252" y="1128">
-skip</text>
-</g>
-</g>
-<path d=" M 192 1090 h 10"/>
-</g>
-<path d=" M 88 1144 v 0 a 12 12 0 0 0 12 12 m 108 0 h 206 m -100 0 l -5 -5 m 0 10 l 5 -5 m 100 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="108" x="100" y="1145"/>
-<text x="154" y="1161">
---recursive</text>
-</g>
-<path d=" M 88 1177 v 0 a 12 12 0 0 0 12 12 m 212 0 h 102 m -48 0 l -5 -5 m 0 10 l 5 -5 m 48 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="212" x="100" y="1178"/>
-<text x="206" y="1194">
---dereference-recursive</text>
-</g>
-<path d=" M 88 1210 v 0 a 12 12 0 0 0 12 12 m 154 0 h 160 m -77 0 l -5 -5 m 0 10 l 5 -5 m 77 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="92" x="100" y="1211"/>
-<text x="146" y="1227">
---include</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="52" x="202" y="1211"/>
-<text x="228" y="1227">
-GLOB</text>
-</g>
-<path d=" M 192 1222 h 10"/>
-</g>
-<path d=" M 88 1243 v 0 a 12 12 0 0 0 12 12 m 154 0 h 160 m -77 0 l -5 -5 m 0 10 l 5 -5 m 77 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="92" x="100" y="1244"/>
-<text x="146" y="1260">
---exclude</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="52" x="202" y="1244"/>
-<text x="228" y="1260">
-GLOB</text>
-</g>
-<path d=" M 192 1255 h 10"/>
-</g>
-<path d=" M 88 1276 v 0 a 12 12 0 0 0 12 12 m 166 0 h 148 m -71 0 l -5 -5 m 0 10 l 5 -5 m 71 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="132" x="100" y="1277"/>
-<text x="166" y="1293">
---exclude-from</text>
-</g>
-<text class="comment" x="254" y="1293">
-ls</text>
-<path d=" M 232 1288 h 10"/>
-</g>
-<path d=" M 88 1309 v 0 a 12 12 0 0 0 12 12 m 186 0 h 128 m -61 0 l -5 -5 m 0 10 l 5 -5 m 61 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="1310"/>
-<text x="162" y="1326">
---exclude-dir</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="52" x="234" y="1310"/>
-<text x="260" y="1326">
-GLOB</text>
-</g>
-<path d=" M 224 1321 h 10"/>
-</g>
-<path d=" M 88 1342 v 0 a 12 12 0 0 0 12 12 m 196 0 h 118 m -56 0 l -5 -5 m 0 10 l 5 -5 m 56 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="196" x="100" y="1343"/>
-<text x="198" y="1359">
---files-without-match</text>
-</g>
-<path d=" M 88 1375 v 0 a 12 12 0 0 0 12 12 m 188 0 h 126 m -60 0 l -5 -5 m 0 10 l 5 -5 m 60 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="188" x="100" y="1376"/>
-<text x="194" y="1392">
---files-with-matches</text>
-</g>
-<path d=" M 88 1408 v 0 a 12 12 0 0 0 12 12 m 76 0 h 238 m -116 0 l -5 -5 m 0 10 l 5 -5 m 116 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="76" x="100" y="1409"/>
-<text x="138" y="1425">
---count</text>
-</g>
-<path d=" M 88 1441 v 0 a 12 12 0 0 0 12 12 m 124 0 h 190 m -92 0 l -5 -5 m 0 10 l 5 -5 m 92 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="124" x="100" y="1442"/>
-<text x="162" y="1458">
---initial-tab</text>
-</g>
-<path d=" M 88 1474 v 0 a 12 12 0 0 0 12 12 m 68 0 h 246 m -120 0 l -5 -5 m 0 10 l 5 -5 m 120 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="68" x="100" y="1475"/>
-<text x="134" y="1491">
---null</text>
-</g>
-<path d=" M 88 1507 v 0 a 12 12 0 0 0 12 12 m 202 0 h 112 m -53 0 l -5 -5 m 0 10 l 5 -5 m 53 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="148" x="100" y="1508"/>
-<text x="174" y="1524">
---before-context</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="44" x="258" y="1508"/>
-<text x="280" y="1524">
-NUM</text>
-</g>
-<path d=" M 248 1519 h 10"/>
-</g>
-<path d=" M 88 1540 v 0 a 12 12 0 0 0 12 12 m 194 0 h 120 m -57 0 l -5 -5 m 0 10 l 5 -5 m 57 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="140" x="100" y="1541"/>
-<text x="170" y="1557">
---after-context</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="44" x="250" y="1541"/>
-<text x="272" y="1557">
-NUM</text>
-</g>
-<path d=" M 240 1552 h 10"/>
-</g>
-<path d=" M 88 1573 v 0 a 12 12 0 0 0 12 12 m 200 0 h 114 m -54 0 l -5 -5 m 0 10 l 5 -5 m 54 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="92" x="100" y="1574"/>
-<text x="146" y="1590">
---context</text>
-</g>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="44" x="202" y="1574"/>
-<text x="224" y="1590">
-NUM</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="44" x="256" y="1574"/>
-<text x="278" y="1590">
-NUM</text>
-</g>
-<path d=" M 246 1585 h 10"/>
-</g>
-<path d=" M 192 1585 h 10"/>
-</g>
-<path d=" M 88 1606 v 0 a 12 12 0 0 0 12 12 m 210 0 h 104 m -49 0 l -5 -5 m 0 10 l 5 -5 m 49 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="156" x="100" y="1607"/>
-<text x="178" y="1623">
---group-separator</text>
-</g>
-<g class="nonterminal">
-<rect height="22" width="44" x="266" y="1607"/>
-<text x="288" y="1623">
-SEP</text>
-</g>
-<path d=" M 256 1618 h 10"/>
-</g>
-<path d=" M 88 1639 v 0 a 12 12 0 0 0 12 12 m 188 0 h 126 m -60 0 l -5 -5 m 0 10 l 5 -5 m 60 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="188" x="100" y="1640"/>
-<text x="194" y="1656">
---no-group-separator</text>
-</g>
-<path d=" M 88 1672 v 12 a 12 12 0 0 0 12 12 m 250 0 h 64 m -29 0 l -5 -5 m 0 10 l 5 -5 m 29 0 a 12 12 0 0 0 12 -12 v -12"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="76" x="100" y="1685"/>
-<text x="138" y="1701">
---color</text>
-</g>
-<g class="optional">
-<path d=" M 186 1696 h 24 m -24 0 a 12 12 0 0 0 12 -12 v 0 a 12 12 0 0 1 12 -12 h 116 m -55 0 l -5 -5 m 0 10 l 5 -5 m 55 0 a 12 12 0 0 1 12 12 v 0 a 12 12 0 0 0 12 12 h -24"/>
-<g class="choice">
-<path d=" M 210 1696 h 24 m 68 0 h 24"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="68" x="234" y="1685"/>
-<text x="268" y="1701">
-always</text>
-</g>
-<path d=" M 210 1696 a 12 12 0 0 1 12 12 v 9 m 92 0 v -9 a 12 12 0 0 1 12 -12"/>
-<path d=" M 222 1717 v 33 m 92 0 v -33"/>
-<path d=" M 222 1717 v 0 a 12 12 0 0 0 12 12 m 60 0 h 8 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="60" x="234" y="1718"/>
-<text x="264" y="1734">
-never</text>
-</g>
-<path d=" M 222 1750 v 0 a 12 12 0 0 0 12 12 m 52 0 h 16 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="52" x="234" y="1751"/>
-<text x="260" y="1767">
-auto</text>
-</g>
-</g>
-</g>
-<path d=" M 176 1696 h 10"/>
-</g>
-<path d=" M 88 1783 v 12 a 12 12 0 0 0 12 12 m 258 0 h 56 m -25 0 l -5 -5 m 0 10 l 5 -5 m 25 0 a 12 12 0 0 0 12 -12 v -12"/>
-<g class="sequence">
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="84" x="100" y="1796"/>
-<text x="142" y="1812">
---colour</text>
-</g>
-<g class="optional">
-<path d=" M 194 1807 h 24 m -24 0 a 12 12 0 0 0 12 -12 v 0 a 12 12 0 0 1 12 -12 h 116 m -55 0 l -5 -5 m 0 10 l 5 -5 m 55 0 a 12 12 0 0 1 12 12 v 0 a 12 12 0 0 0 12 12 h -24"/>
-<g class="choice">
-<path d=" M 218 1807 h 24 m 68 0 h 24"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="68" x="242" y="1796"/>
-<text x="276" y="1812">
-always</text>
-</g>
-<path d=" M 218 1807 a 12 12 0 0 1 12 12 v 9 m 92 0 v -9 a 12 12 0 0 1 12 -12"/>
-<path d=" M 230 1828 v 33 m 92 0 v -33"/>
-<path d=" M 230 1828 v 0 a 12 12 0 0 0 12 12 m 60 0 h 8 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="60" x="242" y="1829"/>
-<text x="272" y="1845">
-never</text>
-</g>
-<path d=" M 230 1861 v 0 a 12 12 0 0 0 12 12 m 52 0 h 16 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="52" x="242" y="1862"/>
-<text x="268" y="1878">
-auto</text>
-</g>
-</g>
-</g>
-<path d=" M 184 1807 h 10"/>
-</g>
-<path d=" M 88 1894 v 0 a 12 12 0 0 0 12 12 m 84 0 h 230 m -112 0 l -5 -5 m 0 10 l 5 -5 m 112 0 a 12 12 0 0 0 12 -12 v 0"/>
-<g class="terminal">
-<rect height="22" rx="10" ry="10" width="84" x="100" y="1895"/>
-<text x="142" y="1911">
---binary</text>
-</g>
-</g>
-</g>
-</g>
-<g class="sequence">
-<g class="nonterminal">
-<rect height="22" width="84" x="484" y="23"/>
-<text x="526" y="39">
-PATTERNS</text>
-</g>
-<g class="repeat">
-<path d=" M 578 34 h 12 m 72 0 h 12 m -12 0 a 12 12 0 0 1 12 12 v 0 a 12 12 0 0 1 -12 12 m 0 0 h -72 m 39 0 l 5 -5 m 0 10 l -5 -5 m -39 0 a 12 12 0 0 1 -12 -12 v 0 a 12 12 0 0 1 12 -12"/>
-<g/>
-<g class="optional">
-<path d=" M 590 34 h 24 m -24 0 a 12 12 0 0 0 12 -12 v 0 a 12 12 0 0 1 12 -12 h 24 a 12 12 0 0 1 12 12 v 0 a 12 12 0 0 0 12 12 h -24"/>
-<text class="comment" x="626" y="39">
-ls</text>
-</g>
-</g>
-<path d=" M 568 34 h 10"/>
-</g>
-<path d=" M 474 34 h 10"/>
-</g>
-<path d=" M 684 34 h 20 m -10 -10 v 20 m 10 -20 v 20"/>
-<path d=" M 30 34 h 10"/>
-<path d=" M 674 34 h 10"/>
-</g>
-</svg>
diff --git a/e2e/test_validation.py b/e2e/test_validation.py
index 62d6adb..b74c21b 100644
--- a/e2e/test_validation.py
+++ b/e2e/test_validation.py
@@ -278,3 +278,23 @@ def test_clashing_variants(complgen_binary_path: Path):
   |                                                          ^^^^^
   |
 """)
+
+
+def test_ambiguous_dfa(complgen_binary_path: Path):
+    r = complgen_check(complgen_binary_path, """
+darcs <SOURCE> ... <DESTINATION>;
+""")
+    assert r.returncode == 1
+    assert r.stderr == snapshot("""\
+warning: undefined nonterminal(s): SOURCE DESTINATION
+1:6:error: Ambiguous grammar.  Matching can't differentiate:
+  |
+1 | darcs <SOURCE> ... <DESTINATION>;
+  |       ^^^^^^^^
+  |
+1:19:error: and:
+  |
+1 | darcs <SOURCE> ... <DESTINATION>;
+  |                    ^^^^^^^^^^^^^
+  |
+""")
diff --git a/examples/darcs.usage b/examples/darcs.usage
index 84c4794..ab8cddd 100644
--- a/examples/darcs.usage
+++ b/examples/darcs.usage
@@ -1,7 +1,7 @@
 darcs help ( ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ... [<DARCS_COMMAND> [<DARCS_SUBCOMMAND>]]  ;
 darcs add ( --boring | ( --case-ok | --reserved-ok ) | ( ( -r | --recursive ) | --not-recursive ) | ( --date-trick | --no-date-trick ) | --repodir <DIRECTORY> | --dry-run | --umask <UMASK> | ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ... <PATH>...;
 darcs remove ( --repodir <DIRECTORY> | --umask <UMASK> | ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ... <PATH>...;
-darcs move ( ( --case-ok | --reserved-ok ) | --repodir <DIRECTORY> | --umask <UMASK> | ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ... <SOURCE> ... <DESTINATION>;
+darcs move ( ( --case-ok | --reserved-ok ) | --repodir <DIRECTORY> | --umask <UMASK> | ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ...;
 darcs replace ( --token-chars <"[CHARS]"> | ( ( -f | --force ) | --no-force ) | --repodir <DIRECTORY> | --ignore-times | --umask <UMASK> | ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ... <OLD> <NEW> <FILE> ...;
 darcs revert ( ( ( -a | --all ) | ( -i | --interactive ) ) | --repodir <DIRECTORY> | --ignore-times | --umask <UMASK> | ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ... [<PATH>]...;
 darcs unrevert ( --ignore-times | ( ( -a | --all ) | ( -i | --interactive ) ) | --repodir <DIRECTORY> | --umask <UMASK> | ( --debug | --debug-verbose | --debug-http | ( -v | --verbose ) | ( -q | --quiet ) | --standard-verbosity ) | --timings | ( --posthook <COMMAND> | --no-posthook ) | ( --prompt-posthook | --run-posthook ) | ( --prehook <COMMAND> | --no-prehook ) | ( --prompt-prehook | --run-prehook ) ) ... ;
diff --git a/proptest-regressions/dfa.txt b/proptest-regressions/dfa.txt
index 88f9b23..52628dc 100644
--- a/proptest-regressions/dfa.txt
+++ b/proptest-regressions/dfa.txt
@@ -14,3 +14,4 @@ cc 65e6e39291e6173e7b5537a9a380dd2fde95048c855ad43a24ff8f2e9ecbac0d # shrinks to
 cc bcad5f86e14429448881e6f6b17fdbb92630580fe3f931c890f47e45a7f78daf # shrinks to (expr, input) = (Alternative(vec![Many1(Box::new(Alternative(vec![Literal(ustr("--quux")), Sequence(vec![Optional(Box::new(Sequence(vec![Many1(Box::new(Many1(Box::new(Alternative(vec![Literal(ustr("--baz")), Variable(ustr("FILE"))]))))), Variable(ustr("FILE"))]))), Sequence(vec![Variable(ustr("FILE")), Literal(ustr("foo"))])])]))), Variable(ustr("FILE"))]), [u!("--quux"), u!("--baz"), u!("anything"), u!("--baz"), u!("anything"), u!("--baz"), u!("anything"), u!("anything"), u!("foo")])
 cc a52f046525ca6f5177ba7bcc93b19ee587157aa6c91a4339480dca2cb20e2e20 # shrinks to (expr, input) = (Alternative(vec![Many1(Box::new(Sequence(vec![Variable(ustr("FILE")), Variable(ustr("FILE"))]))), Variable(ustr("FILE"))]), [u!("anything"), u!("anything"), u!("anything"), u!("anything"), u!("anything"), u!("anything")])
 cc ec60ad08ca4572537d8aee845e67d7fc1aa6d62dbb37be2e25f6feedacbfcf89 # shrinks to (expr, input) = (Sequence(vec![Sequence(vec![Alternative(vec![Many1(Box::new(Many1(Box::new(Literal(ustr("--baz")))))), Variable(ustr("FILE"))]), Literal(ustr("--baz"))]), Many1(Box::new(Alternative(vec![Variable(ustr("FILE")), Variable(ustr("FILE"))])))]), [u!("anything"), u!("--baz"), u!("anything"), u!("anything")])
+cc b86bb96f7474c7a0a23a369c429b491e6ec17e3b09251d762c555fe4773ab14e # shrinks to (expr, arena, input) = (ExprId(575), RefCell { value: [NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Many1(ExprId(0)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Many1(ExprId(2)), Sequence(vec![ExprId(1), ExprId(3)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(5), ExprId(6)]), Many1(ExprId(7)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Many1(ExprId(9)), Many1(ExprId(10)), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Optional(ExprId(12)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(14), ExprId(15)]), Sequence(vec![ExprId(13), ExprId(16)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(18), ExprId(19)]), Optional(ExprId(20)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(22), ExprId(23)]), Optional(ExprId(24)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Many1(ExprId(26)), Optional(ExprId(27)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(29)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(31), ExprId(32)]), Alternative(vec![ExprId(30), ExprId(33)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Many1(ExprId(35)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(37), ExprId(38)]), Alternative(vec![ExprId(36), ExprId(39)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(41), ExprId(42)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(44)), Sequence(vec![ExprId(43), ExprId(45)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Many1(ExprId(48)), Optional(ExprId(49)), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Optional(ExprId(51)), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(53), ExprId(54)]), Alternative(vec![ExprId(52), ExprId(55)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Sequence(vec![ExprId(57), ExprId(58)]), Optional(ExprId(59)), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Optional(ExprId(61)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(63)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(65), ExprId(66)]), Alternative(vec![ExprId(64), ExprId(67)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Optional(ExprId(70)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(78), ExprId(79)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Many1(ExprId(82)), Optional(ExprId(83)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(85), ExprId(86)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(87), ExprId(88)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Optional(ExprId(90)), Optional(ExprId(91)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Optional(ExprId(93)), Optional(ExprId(94)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Many1(ExprId(97)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(98), ExprId(99)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Optional(ExprId(101)), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Many1(ExprId(103)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(104), ExprId(105)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Many1(ExprId(107)), Optional(ExprId(108)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(111)), Many1(ExprId(112)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Sequence(vec![ExprId(115), ExprId(116)]), Many1(ExprId(117)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(119), ExprId(120)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(121), ExprId(122)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Optional(ExprId(124)), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Optional(ExprId(126)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(130), ExprId(131)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(132), ExprId(133)]), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Optional(ExprId(135)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(136), ExprId(137)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Many1(ExprId(139)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Optional(ExprId(141)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(142), ExprId(143)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Optional(ExprId(146)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(148), ExprId(149)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(150), ExprId(151)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Optional(ExprId(154)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(156), ExprId(157)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(159), ExprId(160)]), Sequence(vec![ExprId(158), ExprId(161)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Many1(ExprId(164)), Many1(ExprId(165)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Alternative(vec![ExprId(167), ExprId(168)]), Optional(ExprId(169)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(171)), Optional(ExprId(172)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Optional(ExprId(177)), Sequence(vec![ExprId(176), ExprId(178)]), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(180), ExprId(181)]), Optional(ExprId(182)), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Optional(ExprId(185)), Sequence(vec![ExprId(184), ExprId(186)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Alternative(vec![ExprId(188), ExprId(189)]), Many1(ExprId(190)), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(192), ExprId(193)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Many1(ExprId(195)), Sequence(vec![ExprId(194), ExprId(196)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(198), ExprId(199)]), Optional(ExprId(200)), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Optional(ExprId(202)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(205), ExprId(206)]), Many1(ExprId(207)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(210), ExprId(211)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Optional(ExprId(213)), Alternative(vec![ExprId(212), ExprId(214)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Many1(ExprId(216)), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(217), ExprId(218)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(221)), Alternative(vec![ExprId(220), ExprId(222)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Alternative(vec![ExprId(225), ExprId(226)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(228)), Sequence(vec![ExprId(227), ExprId(229)]), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Many1(ExprId(231)), Many1(ExprId(232)), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Sequence(vec![ExprId(234), ExprId(235)]), Optional(ExprId(236)), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(238), ExprId(239)]), Optional(ExprId(240)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(242), ExprId(243)]), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Optional(ExprId(245)), Sequence(vec![ExprId(244), ExprId(246)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(248), ExprId(249)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(251)), Alternative(vec![ExprId(250), ExprId(252)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Sequence(vec![ExprId(254), ExprId(255)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Optional(ExprId(257)), Alternative(vec![ExprId(256), ExprId(258)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Many1(ExprId(260)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(262), ExprId(263)]), Sequence(vec![ExprId(261), ExprId(264)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(267), ExprId(268)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(270)), Alternative(vec![ExprId(269), ExprId(271)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Many1(ExprId(278)), Optional(ExprId(279)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(281), ExprId(282)]), Many1(ExprId(283)), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(285), ExprId(286)]), Many1(ExprId(287)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(290), ExprId(291)]), Many1(ExprId(292)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(294)), Optional(ExprId(295)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Alternative(vec![ExprId(297), ExprId(298)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(300), ExprId(301)]), Optional(ExprId(302)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Many1(ExprId(305)), Alternative(vec![ExprId(304), ExprId(306)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(309), ExprId(310)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Optional(ExprId(312)), Many1(ExprId(313)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(315)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Many1(ExprId(319)), Alternative(vec![ExprId(318), ExprId(320)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(322)), Many1(ExprId(323)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(325), ExprId(326)]), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(328), ExprId(329)]), Sequence(vec![ExprId(327), ExprId(330)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Many1(ExprId(332)), Many1(ExprId(333)), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(335), ExprId(336)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(337), ExprId(338)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(340), ExprId(341)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(342), ExprId(343)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Optional(ExprId(346)), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(348), ExprId(349)]), Optional(ExprId(350)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Optional(ExprId(356)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Many1(ExprId(358)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(360), ExprId(361)]), Sequence(vec![ExprId(359), ExprId(362)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Optional(ExprId(364)), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(366), ExprId(367)]), Alternative(vec![ExprId(365), ExprId(368)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(370), ExprId(371)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(372), ExprId(373)]), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(376)), Sequence(vec![ExprId(375), ExprId(377)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Many1(ExprId(380)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(381), ExprId(382)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Optional(ExprId(385)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(386), ExprId(387)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(389)), Many1(ExprId(390)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Alternative(vec![ExprId(392), ExprId(393)]), Optional(ExprId(394)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(397), ExprId(398)]), Optional(ExprId(399)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(401), ExprId(402)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(403), ExprId(404)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Many1(ExprId(406)), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(408), ExprId(409)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(411), ExprId(412)]), Alternative(vec![ExprId(410), ExprId(413)]), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Sequence(vec![ExprId(417), ExprId(418)]), Alternative(vec![ExprId(416), ExprId(419)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(421), ExprId(422)]), Optional(ExprId(423)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(426), ExprId(427)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Optional(ExprId(429)), Sequence(vec![ExprId(428), ExprId(430)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(437), ExprId(438)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(439), ExprId(440)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(442)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(443), ExprId(444)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(446), ExprId(447)]), Many1(ExprId(448)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(450)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(451), ExprId(452)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Many1(ExprId(455)), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(458)), Sequence(vec![ExprId(457), ExprId(459)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(463), ExprId(464)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(466)), Alternative(vec![ExprId(465), ExprId(467)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(469), ExprId(470)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(471), ExprId(472)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Optional(ExprId(475)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Optional(ExprId(477)), Alternative(vec![ExprId(476), ExprId(478)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(481), ExprId(482)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(484), ExprId(485)]), Sequence(vec![ExprId(483), ExprId(486)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(488)), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(490), ExprId(491)]), Alternative(vec![ExprId(489), ExprId(492)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Alternative(vec![ExprId(495), ExprId(496)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Optional(ExprId(498)), Sequence(vec![ExprId(497), ExprId(499)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(501), ExprId(502)]), Terminal { term: ustr("--baz"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(504), ExprId(505)]), Sequence(vec![ExprId(503), ExprId(506)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(508)), Many1(ExprId(509)), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(511), ExprId(512)]), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Alternative(vec![ExprId(514), ExprId(515)]), Alternative(vec![ExprId(513), ExprId(516)]), Terminal { term: ustr("bar"), descr: None, fallback: 0, span: None }, NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Many1(ExprId(519)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Alternative(vec![ExprId(521), ExprId(522)]), Optional(ExprId(523)), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Many1(ExprId(525)), Many1(ExprId(526)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(528)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(529), ExprId(530)]), Terminal { term: ustr("foo"), descr: None, fallback: 0, span: None }, Many1(ExprId(532)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(533), ExprId(534)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(536)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(537), ExprId(538)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Optional(ExprId(540)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(541), ExprId(542)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(544)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(545), ExprId(546)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(548)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Sequence(vec![ExprId(549), ExprId(550)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(552)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(553), ExprId(554)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(556)), Terminal { term: ustr("--quux"), descr: None, fallback: 0, span: None }, Sequence(vec![ExprId(557), ExprId(558)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(560)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(561), ExprId(562)]), NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, NontermRef { nonterm: ustr("PATH"), fallback: 0, span: None }, Sequence(vec![ExprId(564), ExprId(565)]), Many1(ExprId(566)), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(568)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(569), ExprId(570)]), NontermRef { nonterm: ustr("FILE"), fallback: 0, span: None }, Many1(ExprId(572)), NontermRef { nonterm: ustr("DIRECTORY"), fallback: 0, span: None }, Sequence(vec![ExprId(573), ExprId(574)])] }, [u!("anything"), u!("anything"), u!("anything")])
diff --git a/src/bash.rs b/src/bash.rs
index bb8660b..5ebc00f 100644
--- a/src/bash.rs
+++ b/src/bash.rs
@@ -3,7 +3,7 @@ use std::io::Write;
 use crate::Result;
 use crate::StateId;
 use crate::dfa::DFA;
-use crate::grammar::CmdRegexDecl;
+use crate::grammar::CmdRegex;
 use crate::grammar::Shell;
 use crate::grammar::Specialization;
 use crate::regex::Input;
@@ -323,8 +323,8 @@ pub fn write_subword_fn<W: Write>(
     let mut fallback_nontails: Vec<HashMap<StateId, Vec<(usize, usize)>>> = Default::default();
     fallback_nontails.resize_with(max_fallback_level + 1, Default::default);
 
-    for (from, input, _) in dfa.iter_transitions() {
-        match input {
+    for (from, input_id, _) in dfa.iter_transitions() {
+        match dfa.get_input(input_id) {
             Input::Literal {
                 literal: lit,
                 description: descr,
@@ -332,7 +332,7 @@ pub fn write_subword_fn<W: Write>(
                 ..
             } => {
                 let literal_id = *literal_id_from_input_description
-                    .get(&(*lit, (*descr).unwrap_or("".into())))
+                    .get(&(*lit, descr.unwrap_or("".into())))
                     .unwrap();
                 fallback_literals[*fallback_level]
                     .entry(from)
@@ -354,7 +354,7 @@ pub fn write_subword_fn<W: Write>(
             Input::Command {
                 cmd,
                 regex:
-                    Some(CmdRegexDecl {
+                    Some(CmdRegex {
                         bash: Some(bash_regex),
                         ..
                     }),
@@ -481,7 +481,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
             }
             Input::Command { cmd, regex, .. } => {
                 id_from_cmd.insert(*cmd);
-                if let Some(CmdRegexDecl {
+                if let Some(CmdRegex {
                     bash: Some(bash_regex),
                     ..
                 }) = regex
@@ -492,7 +492,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
             Input::Subword {
                 subdfa: subdfaid, ..
             } => {
-                let subdfa = dfa.subdfa_interner.lookup(*subdfaid);
+                let subdfa = dfa.subdfas.lookup(*subdfaid);
                 for input in subdfa.iter_inputs() {
                     match input {
                         Input::Nonterminal {
@@ -506,7 +506,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
                         }
                         Input::Command { cmd, regex, .. } => {
                             id_from_cmd.insert(*cmd);
-                            if let Some(CmdRegexDecl {
+                            if let Some(CmdRegex {
                                 bash: Some(bash_regex),
                                 ..
                             }) = regex
@@ -555,7 +555,7 @@ fi
         write_generic_subword_fn(buffer, command)?;
     }
     for (dfaid, id) in &id_from_dfa {
-        let dfa = dfa.subdfa_interner.lookup(*dfaid);
+        let dfa = dfa.subdfas.lookup(*dfaid);
         write_subword_fn(buffer, command, *id, dfa, &id_from_cmd, &id_from_regex)?;
         writeln!(buffer)?;
     }
@@ -579,7 +579,7 @@ fi
 
     writeln!(buffer, r#"    declare -A subword_transitions"#)?;
     for state in dfa.get_all_states() {
-        let subword_transitions = dfa.get_subword_transitions_from(state.try_into().unwrap());
+        let subword_transitions = dfa.get_subword_transitions_from(state);
         if subword_transitions.is_empty() {
             continue;
         }
@@ -682,18 +682,18 @@ fi
     let mut fallback_nontails: Vec<HashMap<StateId, Vec<(usize, usize)>>> = Default::default();
     fallback_nontails.resize_with(max_fallback_level + 1, Default::default);
 
-    for (from, input, _) in dfa.iter_transitions() {
-        match input {
+    for (from, input_id, _) in dfa.iter_transitions() {
+        match dfa.get_input(input_id).clone() {
             Input::Literal {
                 literal: lit,
-                description: descr,
+                description,
                 fallback_level,
                 ..
             } => {
                 let literal_id = *literal_id_from_input_description
-                    .get(&(*lit, (*descr).unwrap_or("".into())))
+                    .get(&(lit, description.unwrap_or("".into())))
                     .unwrap();
-                fallback_literals[*fallback_level]
+                fallback_literals[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(literal_id);
@@ -703,8 +703,8 @@ fi
                 fallback_level,
                 ..
             } => {
-                let subword_id = *id_from_dfa.get(dfa).unwrap();
-                fallback_subwords[*fallback_level]
+                let subword_id = *id_from_dfa.get(&dfa).unwrap();
+                fallback_subwords[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(subword_id);
@@ -715,8 +715,8 @@ fi
                 fallback_level,
                 ..
             } => {
-                let command_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let command_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(command_id);
@@ -724,16 +724,16 @@ fi
             Input::Command {
                 cmd,
                 regex:
-                    Some(CmdRegexDecl {
+                    Some(CmdRegex {
                         bash: Some(bash_regex),
                         ..
                     }),
                 fallback_level,
                 ..
             } => {
-                let cmd_id = id_from_cmd.get_index_of(cmd).unwrap();
-                let regex_id = id_from_regex.get_index_of(bash_regex).unwrap();
-                fallback_nontails[*fallback_level]
+                let cmd_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                let regex_id = id_from_regex.get_index_of(&bash_regex).unwrap();
+                fallback_nontails[fallback_level]
                     .entry(from)
                     .or_default()
                     .push((cmd_id, regex_id));
@@ -746,8 +746,8 @@ fi
                 fallback_level,
                 ..
             } => {
-                let specialized_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let specialized_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(specialized_id);
diff --git a/src/dfa.rs b/src/dfa.rs
index 32e9af3..357422d 100644
--- a/src/dfa.rs
+++ b/src/dfa.rs
@@ -5,9 +5,9 @@ use std::{cmp::Ordering, collections::BTreeSet, hash::Hash, io::Write, rc::Rc};
 use roaring::{MultiOps, RoaringBitmap};
 use ustr::{Ustr, ustr};
 
-use crate::StateId;
-use crate::grammar::{CmdRegexDecl, DFAId, DFAInterner, Shell};
-use crate::regex::{Input, Position, Regex};
+use crate::grammar::{CmdRegex, DFAId, DFAInternPool, Shell};
+use crate::regex::{Input, Position, Regex, diagnostic_display_input};
+use crate::{Error, StateId};
 
 // Every state in a DFA is formally defined to have a transition on *every* input symbol.  In
 // our applications that's not the case, so we add artificial transitions to a special, designated
@@ -21,11 +21,17 @@ pub struct DFA {
 
     // IndexMap is used to keep complgen deterministic
     // https://github.com/adaszko/complgen/issues/60
-    pub transitions: IndexMap<StateId, IndexMap<Input, StateId>>,
+    pub transitions: IndexMap<StateId, IndexMap<Position, StateId>>,
     pub accepting_states: RoaringBitmap,
-    pub input_symbols: Rc<IndexSet<Input>>,
 
-    pub subdfa_interner: DFAInterner,
+    pub input_from_position: Vec<Input>,
+    pub subdfas: DFAInternPool,
+}
+
+impl DFA {
+    pub fn get_input(&self, id: Position) -> &Input {
+        &self.input_from_position[id as usize]
+    }
 }
 
 impl PartialEq for DFA {
@@ -33,7 +39,7 @@ impl PartialEq for DFA {
         self.starting_state == other.starting_state
             && self.transitions == other.transitions
             && self.accepting_states == other.accepting_states
-            && self.input_symbols == other.input_symbols
+            && self.input_from_position == other.input_from_position
     }
 }
 
@@ -51,7 +57,7 @@ impl std::hash::Hash for DFA {
         for elem in &self.accepting_states {
             elem.hash(state);
         }
-        for sym in self.input_symbols.as_ref() {
+        for sym in &self.input_from_position {
             sym.hash(state);
         }
     }
@@ -59,7 +65,7 @@ impl std::hash::Hash for DFA {
 
 // Reference:
 //  * The Dragon Book: 3.9.5 Converting a Regular Expression Directly to a DFA
-fn dfa_from_regex(regex: &Regex, subdfa_interner: DFAInterner) -> DFA {
+fn dfa_from_regex(regex: Regex, subdfas: DFAInternPool) -> DFA {
     let mut unallocated_state_id = FIRST_STATE_ID;
     let combined_starting_state: BTreeSet<Position> = regex.firstpos();
     let combined_starting_state_id = unallocated_state_id;
@@ -69,23 +75,20 @@ fn dfa_from_regex(regex: &Regex, subdfa_interner: DFAInterner) -> DFA {
         IndexMap::from_iter([(combined_starting_state.clone(), combined_starting_state_id)]);
 
     let followpos = regex.followpos();
+    let unique_inputs = regex.get_unique_inputs();
 
-    let mut dtran: IndexMap<StateId, IndexMap<Input, StateId>> = Default::default();
+    let mut dtran: IndexMap<StateId, IndexMap<Position, StateId>> = Default::default();
     let mut unmarked_states: HashSet<BTreeSet<Position>> = Default::default();
     unmarked_states.insert(combined_starting_state.clone());
-    loop {
-        let combined_state = match unmarked_states.iter().next() {
-            Some(state) => state.clone(),
-            None => break,
-        };
+    while let Some(state) = unmarked_states.iter().next() {
+        let combined_state = state.clone();
         unmarked_states.remove(&combined_state);
         let from_combined_state_id = *dstates.get(&combined_state).unwrap();
         let from_entry = dtran.entry(from_combined_state_id).or_default();
-        for input in regex.input_symbols.iter() {
+        for (input, input_id) in &unique_inputs {
             let mut u = RoaringBitmap::new();
             for pos in &combined_state {
-                let pos_usize = usize::try_from(*pos).unwrap();
-                if regex.input_from_position.get(pos_usize) == Some(input)
+                if regex.input_from_position.get(*pos as usize) == Some(input)
                     && let Some(positions) = followpos.get(pos)
                 {
                     u |= positions;
@@ -99,7 +102,7 @@ fn dfa_from_regex(regex: &Regex, subdfa_interner: DFAInterner) -> DFA {
                     unmarked_states.insert(u.clone());
                 }
                 let to_combined_state_id = dstates.get(&u).unwrap();
-                from_entry.insert(input.clone(), *to_combined_state_id);
+                from_entry.insert(*input_id as _, *to_combined_state_id);
             }
         }
     }
@@ -109,7 +112,7 @@ fn dfa_from_regex(regex: &Regex, subdfa_interner: DFAInterner) -> DFA {
         let mut accepting_states = RoaringBitmap::default();
         for (combined_state, state_id) in &dstates {
             if combined_state.contains(&regex.endmarker_position) {
-                accepting_states.insert((*state_id).into());
+                accepting_states.insert(*state_id);
             }
         }
         accepting_states
@@ -119,8 +122,8 @@ fn dfa_from_regex(regex: &Regex, subdfa_interner: DFAInterner) -> DFA {
         starting_state: *dstates.get(&combined_starting_state).unwrap(),
         transitions: dtran,
         accepting_states,
-        input_symbols: Rc::clone(&regex.input_symbols),
-        subdfa_interner,
+        input_from_position: regex.input_from_position,
+        subdfas,
     }
 }
 
@@ -149,7 +152,7 @@ impl std::hash::Hash for HashableRoaringBitmap {
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash)]
-struct SetInternId(usize);
+struct SetId(usize);
 
 #[derive(Default)]
 struct SetInternPool {
@@ -158,7 +161,7 @@ struct SetInternPool {
 }
 
 impl SetInternPool {
-    fn intern(&mut self, set: RoaringBitmap) -> SetInternId {
+    fn intern(&mut self, set: RoaringBitmap) -> SetId {
         let rc = Rc::new(set);
         let id = *self
             .id_from_set
@@ -168,10 +171,10 @@ impl SetInternPool {
                 self.pool.push(rc);
                 id
             });
-        SetInternId(id)
+        SetId(id)
     }
 
-    fn lookup(&self, id: SetInternId) -> Option<Rc<RoaringBitmap>> {
+    fn lookup(&self, id: SetId) -> Option<Rc<RoaringBitmap>> {
         self.pool.get(id.0).cloned()
     }
 }
@@ -180,7 +183,7 @@ impl SetInternPool {
 struct Transition {
     from: StateId,
     to: StateId,
-    input: Input,
+    input: Position,
 }
 
 fn keep_only_states_with_input_transitions(
@@ -188,15 +191,12 @@ fn keep_only_states_with_input_transitions(
     transitions: &[Transition],
     accepting_states: &RoaringBitmap,
 ) -> (Vec<Transition>, RoaringBitmap) {
-    let states_with_input_transition = RoaringBitmap::from_iter(
-        transitions
-            .iter()
-            .map(|transition| u32::from(transition.to)),
-    );
+    let states_with_input_transition =
+        RoaringBitmap::from_iter(transitions.iter().map(|transition| transition.to));
 
     let alive_accepting_states =
         RoaringBitmap::from_sorted_iter(accepting_states.iter().filter(|state| {
-            *state == starting_state.into() || states_with_input_transition.contains(*state)
+            *state == starting_state || states_with_input_transition.contains(*state)
         }))
         .unwrap();
 
@@ -206,8 +206,8 @@ fn keep_only_states_with_input_transitions(
             if transition.from == starting_state {
                 return true;
             }
-            if !states_with_input_transition.contains(transition.from.into())
-                || !states_with_input_transition.contains(transition.to.into())
+            if !states_with_input_transition.contains(transition.from)
+                || !states_with_input_transition.contains(transition.to)
             {
                 return false;
             }
@@ -223,16 +223,13 @@ fn eliminate_nonaccepting_states_without_output_transitions(
     transitions: &[Transition],
     accepting_states: &RoaringBitmap,
 ) -> Vec<Transition> {
-    let states_with_output_transition = RoaringBitmap::from_iter(
-        transitions
-            .iter()
-            .map(|transition| u32::from(transition.from)),
-    );
+    let states_with_output_transition =
+        RoaringBitmap::from_iter(transitions.iter().map(|transition| transition.from));
     let alive_transitions: Vec<Transition> = transitions
         .iter()
         .filter(|transition| {
-            accepting_states.contains(transition.to.into())
-                || states_with_output_transition.contains(transition.to.into())
+            accepting_states.contains(transition.to)
+                || states_with_output_transition.contains(transition.to)
         })
         .cloned()
         .collect();
@@ -282,56 +279,56 @@ fn renumber_states(
         .map(|Transition { from, to, input }| Transition {
             from: *new_from_old_state_id.get(from).unwrap(),
             to: *new_from_old_state_id.get(to).unwrap(),
-            input: input.clone(),
+            input: *input,
         })
         .collect();
 
-    let new_accepting_states: RoaringBitmap =
-        RoaringBitmap::from_iter(accepting_states.iter().map(|old| {
-            u32::from(
-                *new_from_old_state_id
-                    .get(&u16::try_from(old).unwrap())
-                    .unwrap(),
-            )
-        }));
+    let new_accepting_states: RoaringBitmap = RoaringBitmap::from_iter(
+        accepting_states
+            .iter()
+            .map(|old| *new_from_old_state_id.get(&old).unwrap()),
+    );
 
     (new_starting_state, new_transitions, new_accepting_states)
 }
 
 fn hashmap_transitions_from_vec(
     transitions: &[Transition],
-) -> IndexMap<StateId, IndexMap<Input, StateId>> {
-    let mut result: IndexMap<StateId, IndexMap<Input, StateId>> = Default::default();
+) -> IndexMap<StateId, IndexMap<Position, StateId>> {
+    let mut result: IndexMap<StateId, IndexMap<Position, StateId>> = Default::default();
 
     for transition in transitions {
         result
             .entry(transition.from)
             .or_default()
-            .insert(transition.input.clone(), transition.to);
+            .insert(transition.input, transition.to);
     }
 
     result
 }
 
 fn make_transitions_image(
-    transitions: &IndexMap<StateId, IndexMap<Input, StateId>>,
-    input_symbols: Rc<IndexSet<Input>>,
+    transitions: &IndexMap<StateId, IndexMap<Position, StateId>>,
+    input_symbols: &[Input],
 ) -> Vec<Transition> {
     let mut result: Vec<Transition> = Default::default();
     for (from, tos) in transitions {
-        let meaningful_inputs: IndexSet<Input> = tos.keys().cloned().collect();
+        let meaningful_inputs: IndexSet<Position> = tos.keys().cloned().collect();
         for (input, to) in tos {
             result.push(Transition {
                 from: *from,
                 to: *to,
-                input: input.clone(),
+                input: *input,
             });
         }
-        for input in input_symbols.difference(&meaningful_inputs) {
+        for input_id in 0..input_symbols.len() {
+            if meaningful_inputs.contains(&(input_id as Position)) {
+                continue;
+            }
             result.push(Transition {
                 from: *from,
                 to: DEAD_STATE_ID,
-                input: input.clone(),
+                input: input_id as _,
             });
         }
     }
@@ -347,11 +344,10 @@ fn find_bounds(
     group_max: u32,
 ) -> Option<&[Transition]> {
     let inbetween_index = match transitions.binary_search_by(|transition| {
-        let to: u32 = transition.to.into();
-        if to < group_min {
+        if transition.to < group_min {
             return Ordering::Less;
         }
-        if to > group_max {
+        if transition.to > group_max {
             return Ordering::Greater;
         }
         Ordering::Equal
@@ -361,16 +357,14 @@ fn find_bounds(
     };
     let lower_bound = {
         let mut lower_bound = inbetween_index;
-        while lower_bound > 0 && u32::from(transitions[lower_bound - 1].to) >= group_min {
+        while lower_bound > 0 && transitions[lower_bound - 1].to >= group_min {
             lower_bound -= 1;
         }
         lower_bound
     };
     let upper_bound = {
         let mut upper_bound = inbetween_index;
-        while upper_bound < transitions.len() - 1
-            && u32::from(transitions[upper_bound + 1].to) <= group_max
-        {
+        while upper_bound < transitions.len() - 1 && transitions[upper_bound + 1].to <= group_max {
             upper_bound += 1;
         }
         upper_bound
@@ -385,8 +379,8 @@ fn find_bounds(
 //  * https://github.com/BurntSushi/regex-automata/blob/c61a6d0f19b013dc832755375709023dfb9d5a8f/src/dfa/minimize.rs#L87
 fn do_minimize(dfa: DFA) -> DFA {
     let mut pool = SetInternPool::default();
-    let mut partitions: HashSet<SetInternId> = {
-        let dead_state_group = RoaringBitmap::from_iter([u32::from(DEAD_STATE_ID)]);
+    let mut partitions: HashSet<SetId> = {
+        let dead_state_group = RoaringBitmap::from_iter([DEAD_STATE_ID]);
         let all_states = dfa.get_all_states();
         let nonaccepting_states =
             [&all_states, &dfa.accepting_states, &dead_state_group].difference();
@@ -404,12 +398,9 @@ fn do_minimize(dfa: DFA) -> DFA {
         ])
     };
     let mut worklist = partitions.clone();
-    let transitions_image = make_transitions_image(&dfa.transitions, Rc::clone(&dfa.input_symbols));
-    loop {
-        let group_id = match worklist.iter().next() {
-            Some(group_id) => *group_id,
-            None => break,
-        };
+    let transitions_image = make_transitions_image(&dfa.transitions, &dfa.input_from_position);
+    while let Some(group_id) = worklist.iter().next() {
+        let group_id = *group_id;
         worklist.remove(&group_id);
         let group = pool.lookup(group_id).unwrap();
         let group_min = group.min().unwrap();
@@ -420,20 +411,20 @@ fn do_minimize(dfa: DFA) -> DFA {
             None => continue,
         };
 
-        let transitions_to_group: HashMap<Input, RoaringBitmap> = {
-            let mut group_transitions: HashMap<Input, RoaringBitmap> = Default::default();
+        let transitions_to_group: HashMap<Position, RoaringBitmap> = {
+            let mut group_transitions: HashMap<Position, RoaringBitmap> = Default::default();
             for transition in transitions {
-                if group.contains(transition.to.into()) {
+                if group.contains(transition.to) {
                     group_transitions
-                        .entry(transition.input.clone())
+                        .entry(transition.input)
                         .or_default()
-                        .insert(transition.from.into());
+                        .insert(transition.from);
                 }
             }
             group_transitions
         };
         for from_states in transitions_to_group.values() {
-            let overlapping_sets: Vec<SetInternId> = partitions
+            let overlapping_sets: Vec<SetId> = partitions
                 .iter()
                 .filter(|set_id| !pool.lookup(**set_id).unwrap().is_disjoint(from_states))
                 .copied()
@@ -493,12 +484,7 @@ fn do_minimize(dfa: DFA) -> DFA {
     let accepting_states = {
         let mut accepting_states: RoaringBitmap = Default::default();
         for state_id in &dfa.accepting_states {
-            accepting_states.insert(
-                (*representative_id_from_state_id
-                    .get(&u16::try_from(state_id).unwrap())
-                    .unwrap())
-                .into(),
-            );
+            accepting_states.insert(*representative_id_from_state_id.get(&state_id).unwrap());
         }
         accepting_states
     };
@@ -511,7 +497,7 @@ fn do_minimize(dfa: DFA) -> DFA {
                 transitions.push(Transition {
                     from: *from,
                     to: *representative,
-                    input: input.clone(),
+                    input: *input,
                 });
             }
         }
@@ -529,8 +515,8 @@ fn do_minimize(dfa: DFA) -> DFA {
         starting_state,
         transitions,
         accepting_states,
-        input_symbols: Rc::clone(&dfa.input_symbols),
-        subdfa_interner: dfa.subdfa_interner,
+        input_from_position: dfa.input_from_position,
+        subdfas: dfa.subdfas,
     }
 }
 
@@ -539,15 +525,15 @@ fn do_to_dot<W: Write>(
     dfa: &DFA,
     identifiers_prefix: &str,
     recursion_level: usize,
-) -> std::result::Result<(), std::io::Error> {
+) -> crate::Result<()> {
     let indentation = format!("\t{}", str::repeat("\t", recursion_level));
 
     let id_from_dfa = dfa.get_subwords(0);
 
-    if dfa.accepting_states.contains(dfa.starting_state.into()) {
-        writeln!(output, "{indentation}node [shape = doubleoctagon];")?;
+    if dfa.accepting_states.contains(dfa.starting_state) {
+        writeln!(output, "{indentation}node [shape=doubleoctagon];")?;
     } else {
-        writeln!(output, "{indentation}node [shape = octagon];")?;
+        writeln!(output, "{indentation}node [shape=octagon];")?;
     }
     writeln!(
         output,
@@ -557,11 +543,11 @@ fn do_to_dot<W: Write>(
 
     let regular_states = {
         let mut states = [&dfa.get_all_states(), &dfa.accepting_states].difference();
-        states.remove(dfa.starting_state.into());
+        states.remove(dfa.starting_state);
         states
     };
 
-    writeln!(output, "{indentation}node [shape = circle];")?;
+    writeln!(output, "{indentation}node [shape=circle];")?;
     for state in regular_states {
         writeln!(
             output,
@@ -572,7 +558,7 @@ fn do_to_dot<W: Write>(
 
     writeln!(output)?;
 
-    writeln!(output, "{indentation}node [shape = doublecircle];")?;
+    writeln!(output, "{indentation}node [shape=doublecircle];")?;
     for state in &dfa.accepting_states {
         writeln!(
             output,
@@ -592,7 +578,7 @@ fn do_to_dot<W: Write>(
         writeln!(output, "{indentation}\tcolor=grey91;")?;
         writeln!(output, "{indentation}\tstyle=filled;")?;
         let subdfa_identifiers_prefix = &format!("{subdfa_id}_");
-        let subdfa = dfa.subdfa_interner.lookup(*subdfaid);
+        let subdfa = dfa.subdfas.lookup(*subdfaid);
         do_to_dot(
             output,
             subdfa,
@@ -603,10 +589,15 @@ fn do_to_dot<W: Write>(
     }
 
     for (from, tos) in &dfa.transitions {
-        for (input, to) in tos {
+        for (input_id, to) in tos {
+            let input = dfa.get_input(*input_id);
             match input {
                 Input::Literal { .. } | Input::Nonterminal { .. } | Input::Command { .. } => {
-                    let label = format!("{}", input).replace('\"', "\\\"");
+                    let label = {
+                        let mut buffer = String::new();
+                        diagnostic_display_input(&mut buffer, input)?;
+                        buffer.replace('\"', "\\\"")
+                    };
                     writeln!(
                         output,
                         "{indentation}_{identifiers_prefix}{} -> _{identifiers_prefix}{} [label=\"{}\"];",
@@ -616,7 +607,7 @@ fn do_to_dot<W: Write>(
                 Input::Subword {
                     subdfa: subdfaid, ..
                 } => {
-                    let subdfa = dfa.subdfa_interner.lookup(*subdfaid);
+                    let subdfa = dfa.subdfas.lookup(*subdfaid);
                     let subdfa_id = *id_from_dfa.get(subdfaid).unwrap();
                     let subdfa_identifiers_prefix = &format!("{subdfa_id}_");
                     writeln!(
@@ -641,7 +632,8 @@ fn do_to_dot<W: Write>(
 
 fn do_get_subdfa_command_transitions(dfa: &DFA, result: &mut Vec<(StateId, Ustr)>) {
     for (from, tos) in &dfa.transitions {
-        for (input, _) in tos {
+        for (input_id, _) in tos {
+            let input = dfa.get_input(*input_id);
             let cmd = match input {
                 Input::Command { cmd, .. } => *cmd,
                 Input::Subword { .. } => unreachable!(),
@@ -654,8 +646,14 @@ fn do_get_subdfa_command_transitions(dfa: &DFA, result: &mut Vec<(StateId, Ustr)
 }
 
 impl DFA {
-    pub fn from_regex(regex: &Regex, subdfa_interner: DFAInterner) -> Self {
-        dfa_from_regex(regex, subdfa_interner)
+    pub fn from_regex_strict(regex: Regex, subdfas: DFAInternPool) -> crate::Result<Self> {
+        let dfa = Self::from_regex(regex, subdfas);
+        dfa.check_ambiguity_best_effort()?;
+        Ok(dfa)
+    }
+
+    pub fn from_regex(regex: Regex, subdfas: DFAInternPool) -> Self {
+        dfa_from_regex(regex, subdfas)
     }
 
     pub fn minimize(self) -> Self {
@@ -665,7 +663,8 @@ impl DFA {
     pub fn accepts_str(&self, mut input: &str, shell: Shell) -> bool {
         let mut current_state = self.starting_state;
         'outer: while !input.is_empty() {
-            for (transition_input, to) in self.iter_transitions_from(current_state) {
+            for (transition_input_id, to) in self.iter_transitions_from(current_state) {
+                let transition_input = self.get_input(transition_input_id);
                 if let Input::Literal { literal, .. } = transition_input {
                     let s = literal.as_str();
                     if input.starts_with(s) {
@@ -676,7 +675,8 @@ impl DFA {
                 }
             }
 
-            for (transition_input, to) in self.iter_transitions_from(current_state) {
+            for (transition_input_id, to) in self.iter_transitions_from(current_state) {
+                let transition_input = self.get_input(transition_input_id);
                 if transition_input.is_ambiguous(shell) {
                     current_state = to;
                     break 'outer;
@@ -685,34 +685,87 @@ impl DFA {
 
             break;
         }
-        self.accepting_states.contains(current_state.into())
+        self.accepting_states.contains(current_state)
+    }
+
+    fn do_check_ambiguity_best_effort(
+        &self,
+        state: StateId,
+        visited: &mut RoaringBitmap,
+        path: &mut Vec<Input>,
+    ) -> crate::Result<()> {
+        let mut ambiguous_inputs: Vec<Input> = Default::default();
+        for (input_id, _) in self.iter_transitions_from(state) {
+            let input = self.get_input(input_id);
+            match input {
+                Input::Literal { .. } => {}
+                Input::Nonterminal { .. } => ambiguous_inputs.push(input.clone()),
+                Input::Subword {
+                    subdfa: subdfa_id, ..
+                } => {
+                    let subdfa = self.subdfas.lookup(*subdfa_id);
+                    subdfa.check_ambiguity_best_effort()?
+                }
+                Input::Command { regex: None, .. } => ambiguous_inputs.push(input.clone()),
+                Input::Command {
+                    regex: Some(..), ..
+                } => {}
+            }
+        }
+        if ambiguous_inputs.len() >= 2 {
+            return Err(Error::AmbiguousDFA(
+                path.to_owned().into_boxed_slice(),
+                ambiguous_inputs.into_boxed_slice(),
+            ));
+        }
+        for (input_id, to) in self.iter_transitions_from(state) {
+            if !visited.contains(to) {
+                visited.insert(to);
+                let input = self.get_input(input_id);
+                path.push(input.clone());
+                self.do_check_ambiguity_best_effort(to, visited, path)?;
+                path.pop();
+            }
+        }
+        Ok(())
+    }
+
+    pub fn check_ambiguity_best_effort(&self) -> crate::Result<()> {
+        let mut visited: RoaringBitmap = Default::default();
+        let mut path: Vec<Input> = Default::default();
+        self.do_check_ambiguity_best_effort(self.starting_state, &mut visited, &mut path)?;
+        Ok(())
     }
 
     pub fn iter_inputs(&self) -> impl Iterator<Item = &Input> + '_ {
-        self.iter_transitions().map(|(_, input, _)| input)
+        self.iter_transitions()
+            .map(|(_, input_id, _)| self.get_input(input_id))
     }
 
-    pub fn iter_froms_inputs(&self) -> impl Iterator<Item = (StateId, Input)> + '_ {
+    pub fn iter_froms_inputs(&self) -> impl Iterator<Item = (StateId, Position)> + '_ {
         self.transitions
             .iter()
-            .flat_map(|(from, tos)| tos.iter().map(|(input, _)| (*from, input.clone())))
+            .flat_map(|(from, tos)| tos.iter().map(|(input, _)| (*from, *input)))
     }
 
-    pub fn iter_transitions_from(&self, from: StateId) -> impl Iterator<Item = (Input, StateId)> {
+    pub fn iter_transitions_from(
+        &self,
+        from: StateId,
+    ) -> impl Iterator<Item = (Position, StateId)> {
         match self.transitions.get(&from) {
             Some(transitions) => transitions.clone().into_iter(),
-            None => IndexMap::<Input, StateId>::default().into_iter(),
+            None => IndexMap::<Position, StateId>::default().into_iter(),
         }
     }
 
-    pub fn iter_transitions(&self) -> impl Iterator<Item = (StateId, &Input, StateId)> + '_ {
+    pub fn iter_transitions(&self) -> impl Iterator<Item = (StateId, Position, StateId)> + '_ {
         self.transitions
             .iter()
-            .flat_map(|(from, tos)| tos.iter().map(|(input, to)| (*from, input, *to)))
+            .flat_map(|(from, tos)| tos.iter().map(|(input, to)| (*from, *input, *to)))
     }
 
     pub fn get_all_literals(&self) -> Vec<(Ustr, Option<Ustr>)> {
-        self.input_symbols
+        self.input_from_position
             .iter()
             .filter_map(|input| match input {
                 Input::Literal {
@@ -730,12 +783,13 @@ impl DFA {
     pub fn get_subword_command_transitions(&self) -> HashMap<DFAId, Vec<(StateId, Ustr)>> {
         let mut subdfas: HashMap<DFAId, Vec<(StateId, Ustr)>> = Default::default();
         for (_, tos) in &self.transitions {
-            for (input, _) in tos {
+            for (input_id, _) in tos {
+                let input = self.get_input(*input_id);
                 match input {
                     Input::Subword {
                         subdfa: subdfaid, ..
                     } => {
-                        let subdfa = self.subdfa_interner.lookup(*subdfaid);
+                        let subdfa = self.subdfas.lookup(*subdfaid);
                         if subdfas.contains_key(subdfaid) {
                             continue;
                         }
@@ -746,7 +800,7 @@ impl DFA {
                     Input::Command { .. } => continue,
                     Input::Nonterminal { .. } => continue,
                     Input::Literal { .. } => continue,
-                };
+                }
             }
         }
         subdfas
@@ -759,15 +813,18 @@ impl DFA {
         };
         let transitions: Vec<(Ustr, Ustr, StateId)> = map
             .iter()
-            .filter_map(|(input, to)| match input {
-                Input::Literal {
-                    literal: input,
-                    description,
-                    ..
-                } => Some((*input, description.unwrap_or(ustr("")), *to)),
-                Input::Subword { .. } => None,
-                Input::Nonterminal { .. } => None,
-                Input::Command { .. } => None,
+            .filter_map(|(input_id, to)| {
+                let input = self.get_input(*input_id);
+                match input {
+                    Input::Literal {
+                        literal: input,
+                        description,
+                        ..
+                    } => Some((*input, description.unwrap_or(ustr("")), *to)),
+                    Input::Subword { .. } => None,
+                    Input::Nonterminal { .. } => None,
+                    Input::Command { .. } => None,
+                }
             })
             .collect();
         transitions
@@ -780,23 +837,26 @@ impl DFA {
         };
         let transitions: Vec<(Ustr, StateId)> = map
             .iter()
-            .filter_map(|(input, to)| match input {
-                Input::Command {
-                    cmd: _,
-                    regex:
-                        Some(CmdRegexDecl {
-                            bash: Some(regex), ..
-                        }),
-                    ..
-                } => Some((*regex, *to)),
-                Input::Command { regex: None, .. } => None,
-                Input::Command {
-                    regex: Some(CmdRegexDecl { bash: None, .. }),
-                    ..
-                } => None,
-                Input::Literal { .. } => None,
-                Input::Subword { .. } => None,
-                Input::Nonterminal { .. } => None,
+            .filter_map(|(input_id, to)| {
+                let input = self.get_input(*input_id);
+                match input {
+                    Input::Command {
+                        cmd: _,
+                        regex:
+                            Some(CmdRegex {
+                                bash: Some(regex), ..
+                            }),
+                        ..
+                    } => Some((*regex, *to)),
+                    Input::Command { regex: None, .. } => None,
+                    Input::Command {
+                        regex: Some(CmdRegex { bash: None, .. }),
+                        ..
+                    } => None,
+                    Input::Literal { .. } => None,
+                    Input::Subword { .. } => None,
+                    Input::Nonterminal { .. } => None,
+                }
             })
             .collect();
         transitions
@@ -809,18 +869,18 @@ impl DFA {
         };
         let transitions: Vec<(Ustr, StateId)> = map
             .iter()
-            .filter_map(|(input, to)| match input {
+            .filter_map(|(input_id, to)| match self.get_input(*input_id) {
                 Input::Command {
                     cmd: _,
                     regex:
-                        Some(CmdRegexDecl {
+                        Some(CmdRegex {
                             fish: Some(regex), ..
                         }),
                     ..
                 } => Some((*regex, *to)),
                 Input::Command { regex: None, .. } => None,
                 Input::Command {
-                    regex: Some(CmdRegexDecl { fish: None, .. }),
+                    regex: Some(CmdRegex { fish: None, .. }),
                     ..
                 } => None,
                 Input::Literal { .. } => None,
@@ -838,18 +898,18 @@ impl DFA {
         };
         let transitions: Vec<(Ustr, StateId)> = map
             .iter()
-            .filter_map(|(input, to)| match input {
+            .filter_map(|(input_id, to)| match self.get_input(*input_id) {
                 Input::Command {
                     cmd: _,
                     regex:
-                        Some(CmdRegexDecl {
+                        Some(CmdRegex {
                             zsh: Some(regex), ..
                         }),
                     ..
                 } => Some((*regex, *to)),
                 Input::Command { regex: None, .. } => None,
                 Input::Command {
-                    regex: Some(CmdRegexDecl { zsh: None, .. }),
+                    regex: Some(CmdRegex { zsh: None, .. }),
                     ..
                 } => None,
                 Input::Literal { .. } => None,
@@ -867,7 +927,7 @@ impl DFA {
         };
         let transitions: Vec<(DFAId, StateId)> = map
             .iter()
-            .filter_map(|(input, to)| match input {
+            .filter_map(|(input_id, to)| match self.get_input(*input_id) {
                 Input::Subword { subdfa: dfa, .. } => Some((*dfa, *to)),
                 Input::Literal { .. } => None,
                 Input::Nonterminal { .. } => None,
@@ -879,10 +939,7 @@ impl DFA {
 
     pub fn has_subword_transitions(&self) -> bool {
         for state in self.get_all_states() {
-            if !self
-                .get_subword_transitions_from(state.try_into().unwrap())
-                .is_empty()
-            {
+            if !self.get_subword_transitions_from(state).is_empty() {
                 return true;
             }
         }
@@ -892,10 +949,10 @@ impl DFA {
     pub fn get_all_states(&self) -> RoaringBitmap {
         let mut states: RoaringBitmap = Default::default();
         self.iter_transitions().for_each(|(from, _, to)| {
-            states.insert(from.into());
-            states.insert(to.into());
+            states.insert(from);
+            states.insert(to);
         });
-        states.insert(DEAD_STATE_ID.into());
+        states.insert(DEAD_STATE_ID);
         states
     }
 
@@ -904,7 +961,8 @@ impl DFA {
         shell: Shell,
     ) -> impl Iterator<Item = (StateId, StateId)> + '_ {
         self.iter_transitions()
-            .filter_map(move |(from, input, to)| {
+            .filter_map(move |(from, input_id, to)| {
+                let input = self.get_input(input_id);
                 if input.is_ambiguous(shell) {
                     Some((from, to))
                 } else {
@@ -917,8 +975,8 @@ impl DFA {
         let mut unallocated_id = first_id;
         let mut result: IndexMap<DFAId, usize> = Default::default();
         for (_, tos) in &self.transitions {
-            for (input, _) in tos {
-                let dfa = match input {
+            for (input_id, _) in tos {
+                let dfa = match self.get_input(*input_id) {
                     Input::Subword { subdfa, .. } => subdfa,
                     Input::Nonterminal { .. } => continue,
                     Input::Command { .. } => continue,
@@ -940,8 +998,8 @@ impl DFA {
             .max()
     }
 
-    pub fn to_dot<W: Write>(&self, output: &mut W) -> std::result::Result<(), std::io::Error> {
-        writeln!(output, "digraph nfa {{")?;
+    pub fn to_dot<W: Write>(&self, output: &mut W) -> crate::Result<()> {
+        writeln!(output, "digraph dfa {{")?;
         writeln!(output, "\trankdir=LR;")?;
         do_to_dot(output, self, "", 0)?;
         writeln!(output, "}}")?;
@@ -949,10 +1007,7 @@ impl DFA {
     }
 
     #[allow(dead_code)]
-    pub fn to_dot_file<P: AsRef<std::path::Path>>(
-        &self,
-        path: P,
-    ) -> std::result::Result<(), std::io::Error> {
+    pub fn to_dot_file<P: AsRef<std::path::Path>>(&self, path: P) -> crate::Result<()> {
         let mut file = std::fs::File::create(path)?;
         self.to_dot(&mut file)?;
         Ok(())
@@ -988,21 +1043,6 @@ mod tests {
         }
     }
 
-    impl Transition {
-        fn new(from: StateId, input: &str, to: StateId) -> Self {
-            Self {
-                from,
-                input: Input::Literal {
-                    literal: ustr::ustr(input),
-                    description: None,
-                    fallback_level: 0,
-                    span: None,
-                },
-                to,
-            }
-        }
-    }
-
     impl DFA {
         pub fn accepts(&self, inputs: &[&str], shell: Shell) -> Result<bool, TestCaseError> {
             let mut input_index = 0;
@@ -1012,7 +1052,8 @@ mod tests {
                     break;
                 }
 
-                for (transition_input, to) in self.iter_transitions_from(current_state) {
+                for (transition_input_id, to) in self.iter_transitions_from(current_state) {
+                    let transition_input = self.get_input(transition_input_id);
                     if let Input::Literal { literal, .. } = transition_input {
                         if inputs[input_index] == literal.as_str() {
                             input_index += 1;
@@ -1022,9 +1063,10 @@ mod tests {
                     }
                 }
 
-                for (transition_input, to) in self.iter_transitions_from(current_state) {
+                for (transition_input_id, to) in self.iter_transitions_from(current_state) {
+                    let transition_input = self.get_input(transition_input_id);
                     if let Input::Subword { subdfa, .. } = transition_input {
-                        let dfa = self.subdfa_interner.lookup(subdfa);
+                        let dfa = self.subdfas.lookup(*subdfa);
                         if dfa.accepts_str(inputs[input_index], shell) {
                             input_index += 1;
                             current_state = to;
@@ -1033,16 +1075,17 @@ mod tests {
                     }
                 }
 
-                let anys: Vec<(Input, StateId)> = self
+                let anys: Vec<(Position, StateId)> = self
                     .iter_transitions_from(current_state)
-                    .filter(|(input, _)| input.is_ambiguous(shell))
+                    .filter(|(input_id, _)| self.get_input(*input_id).is_ambiguous(shell))
                     .map(|(k, v)| (k.clone(), v))
                     .collect();
                 // It's ambiguous which transition to take if there are two transitions
                 // representing a nonterminal.
-                prop_assume!(anys.len() <= 1);
+                assert!(anys.len() <= 1);
 
-                for (transition_input, to) in anys {
+                for (transition_input_id, to) in anys {
+                    let transition_input = self.get_input(transition_input_id);
                     if transition_input.is_ambiguous(shell) {
                         input_index += 1;
                         current_state = to;
@@ -1055,21 +1098,7 @@ mod tests {
             Ok(self.accepting_states.contains(current_state.into()))
         }
 
-        fn get_transitions(&self) -> Vec<Transition> {
-            let mut result: Vec<Transition> = Default::default();
-            for (from, tos) in &self.transitions {
-                for (input, to) in tos {
-                    result.push(Transition {
-                        from: *from,
-                        to: *to,
-                        input: input.clone(),
-                    });
-                }
-            }
-            result
-        }
-
-        pub fn has_transition(&self, from: StateId, input: Input, to: StateId) -> bool {
+        pub fn has_transition(&self, from: StateId, input: Position, to: StateId) -> bool {
             *self.transitions.get(&from).unwrap().get(&input).unwrap() == to
         }
     }
@@ -1080,9 +1109,21 @@ mod tests {
         let expr = alloc(&mut arena, Expr::term("foo"));
         let specs = UstrMap::default();
         let regex = Regex::from_expr(expr, &arena, &specs).unwrap();
-        let dfa = DFA::from_regex(&regex, DFAInterner::default());
-        let transitions = dfa.get_transitions();
-        assert_eq!(transitions, vec![Transition::new(1, "foo", 2)]);
+        assert!(matches!(
+            regex.ensure_ambiguous_inputs_tail_only(Shell::Bash),
+            Ok(())
+        ));
+        assert!(matches!(regex.check_clashing_variants(), Ok(())));
+        let dfa = DFA::from_regex_strict(regex, DFAInternPool::default()).unwrap();
+        let foo = Input::literal("foo");
+        let (foo_id, _) = dfa
+            .input_from_position
+            .iter()
+            .find_position(|e| e == &&foo)
+            .unwrap();
+        assert_eq!(dfa.transitions.len(), 2);
+        let tos: IndexMap<Position, StateId> = IndexMap::from_iter([(foo_id as _, 2)]);
+        assert_eq!(*dfa.transitions.get(&1).unwrap(), tos);
         assert_eq!(dfa.accepting_states, RoaringBitmap::from_iter([2]));
         assert_eq!(dfa.starting_state, 1);
     }
@@ -1260,7 +1301,7 @@ mod tests {
         max_width: usize,
         output: &mut Vec<Ustr>,
     ) {
-        match &arena.borrow()[expr.to_index()] {
+        match &arena.borrow()[expr] {
             Terminal { term, .. } => output.push(*term),
             Subword {
                 phase: SubwordCompilationPhase::Expr(e),
@@ -1320,10 +1361,10 @@ mod tests {
 
     // Produce an arbitrary sequence matching `e`.
     pub fn arb_expr_match(
-        inputs: Rc<Vec<Ustr>>,
-        nonterminals: Rc<Vec<Ustr>>,
         remaining_depth: usize,
         max_width: usize,
+        inputs: Rc<Vec<Ustr>>,
+        nonterminals: Rc<Vec<Ustr>>,
     ) -> BoxedStrategy<(ExprId, Rc<RefCell<Vec<Expr>>>, Vec<Ustr>)> {
         let arena = Rc::new(RefCell::new(vec![]));
         arb_expr(
@@ -1337,25 +1378,311 @@ mod tests {
         .boxed()
     }
 
+    /// Illustrates why trying to detect matching ambiguities at Regex stage is futile, or to be
+    /// more precise, is doomed to work duplication with transforming regex into a DFA and also is
+    /// necessarily complicated.  The Expr below leads to generating a DFA that's ambiguous but it
+    /// isn't readily apparent just from examining Regex::followpos() paths.  The ambiguity arises
+    /// from having two separate "--baz" in two separate places in the regex tree.  It leads to a
+    /// DFA state where we're trying to make a transition based on whether the input is <FILE> or
+    /// <DIRECTORY> -- i.e. something that can't be done.  Better way is to perform ambiguity
+    /// detection at the DFA compilation phase (likely before minimization) and that's what
+    /// subsequent commits should implement.  It was found by proptest.
+    #[test]
+    fn followpos_ambiuity_detection_counterexample() {
+        let expr = ExprId(94);
+        let arena = RefCell::new(vec![
+            NontermRef {
+                nonterm: ustr("FILE"),
+                fallback: 0,
+                span: None,
+            },
+            Optional(ExprId(0)),
+            Optional(ExprId(1)),
+            Optional(ExprId(2)),
+            Optional(ExprId(3)),
+            NontermRef {
+                nonterm: ustr("FILE"),
+                fallback: 0,
+                span: None,
+            },
+            Optional(ExprId(5)),
+            Alternative(vec![ExprId(4), ExprId(6)]),
+            NontermRef {
+                nonterm: ustr("DIRECTORY"),
+                fallback: 0,
+                span: None,
+            },
+            Terminal {
+                term: ustr("bar"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Alternative(vec![ExprId(8), ExprId(9)]),
+            NontermRef {
+                nonterm: ustr("DIRECTORY"),
+                fallback: 0,
+                span: None,
+            },
+            Optional(ExprId(11)),
+            Alternative(vec![ExprId(10), ExprId(12)]),
+            NontermRef {
+                nonterm: ustr("DIRECTORY"),
+                fallback: 0,
+                span: None,
+            },
+            NontermRef {
+                nonterm: ustr("FILE"),
+                fallback: 0,
+                span: None,
+            },
+            Alternative(vec![ExprId(14), ExprId(15)]),
+            Terminal {
+                term: ustr("foo"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Terminal {
+                term: ustr("bar"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Alternative(vec![ExprId(17), ExprId(18)]),
+            Sequence(vec![ExprId(16), ExprId(19)]),
+            Sequence(vec![ExprId(13), ExprId(20)]),
+            NontermRef {
+                nonterm: ustr("PATH"),
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(21), ExprId(22)]),
+            Terminal {
+                term: ustr("--baz"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Many1(ExprId(24)),
+            Many1(ExprId(25)),
+            Sequence(vec![ExprId(23), ExprId(26)]),
+            Sequence(vec![ExprId(7), ExprId(27)]),
+            Many1(ExprId(28)),
+            Many1(ExprId(29)),
+            Terminal {
+                term: ustr("--baz"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            NontermRef {
+                nonterm: ustr("PATH"),
+                fallback: 0,
+                span: None,
+            },
+            Many1(ExprId(32)),
+            Optional(ExprId(33)),
+            Many1(ExprId(34)),
+            NontermRef {
+                nonterm: ustr("FILE"),
+                fallback: 0,
+                span: None,
+            },
+            Many1(ExprId(36)),
+            Sequence(vec![ExprId(35), ExprId(37)]),
+            Optional(ExprId(38)),
+            Optional(ExprId(39)),
+            Sequence(vec![ExprId(31), ExprId(40)]),
+            Sequence(vec![ExprId(30), ExprId(41)]),
+            Terminal {
+                term: ustr("bar"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Many1(ExprId(43)),
+            NontermRef {
+                nonterm: ustr("PATH"),
+                fallback: 0,
+                span: None,
+            },
+            Alternative(vec![ExprId(44), ExprId(45)]),
+            NontermRef {
+                nonterm: ustr("FILE"),
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(46), ExprId(47)]),
+            NontermRef {
+                nonterm: ustr("PATH"),
+                fallback: 0,
+                span: None,
+            },
+            Terminal {
+                term: ustr("bar"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(49), ExprId(50)]),
+            Sequence(vec![ExprId(48), ExprId(51)]),
+            Many1(ExprId(52)),
+            Terminal {
+                term: ustr("foo"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            NontermRef {
+                nonterm: ustr("DIRECTORY"),
+                fallback: 0,
+                span: None,
+            },
+            Alternative(vec![ExprId(54), ExprId(55)]),
+            Optional(ExprId(56)),
+            Many1(ExprId(57)),
+            Terminal {
+                term: ustr("bar"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Optional(ExprId(59)),
+            Optional(ExprId(60)),
+            Sequence(vec![ExprId(58), ExprId(61)]),
+            Terminal {
+                term: ustr("foo"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Many1(ExprId(63)),
+            NontermRef {
+                nonterm: ustr("PATH"),
+                fallback: 0,
+                span: None,
+            },
+            Many1(ExprId(65)),
+            Sequence(vec![ExprId(64), ExprId(66)]),
+            Many1(ExprId(67)),
+            Alternative(vec![ExprId(62), ExprId(68)]),
+            NontermRef {
+                nonterm: ustr("DIRECTORY"),
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(69), ExprId(70)]),
+            NontermRef {
+                nonterm: ustr("PATH"),
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(71), ExprId(72)]),
+            Many1(ExprId(73)),
+            Many1(ExprId(74)),
+            Terminal {
+                term: ustr("bar"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Optional(ExprId(76)),
+            Terminal {
+                term: ustr("--baz"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            NontermRef {
+                nonterm: ustr("DIRECTORY"),
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(78), ExprId(79)]),
+            Terminal {
+                term: ustr("--quux"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Optional(ExprId(81)),
+            Many1(ExprId(82)),
+            Terminal {
+                term: ustr("--quux"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Optional(ExprId(84)),
+            Alternative(vec![ExprId(83), ExprId(85)]),
+            Alternative(vec![ExprId(80), ExprId(86)]),
+            Optional(ExprId(87)),
+            Optional(ExprId(88)),
+            Terminal {
+                term: ustr("--baz"),
+                descr: None,
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(89), ExprId(90)]),
+            NontermRef {
+                nonterm: ustr("FILE"),
+                fallback: 0,
+                span: None,
+            },
+            Sequence(vec![ExprId(91), ExprId(92)]),
+            Sequence(vec![ExprId(77), ExprId(93)]),
+        ]);
+        //expr_to_dot_file("expr.dot", expr, &arena.borrow()).unwrap();
+        let specs = UstrMap::default();
+        let regex = Regex::from_expr(expr, &arena.borrow(), &specs).unwrap();
+
+        //dbg!(&regex.firstpos());
+        //dbg!(&regex.followpos());
+        //dbg!(&regex.input_from_position);
+
+        assert!(matches!(
+            regex.ensure_ambiguous_inputs_tail_only(Shell::Bash),
+            Ok(())
+        ));
+        assert!(matches!(regex.check_clashing_variants(), Ok(())));
+
+        //regex.to_dot_file("regex.dot").unwrap();
+        assert!(matches!(
+            DFA::from_regex_strict(regex, DFAInternPool::default()),
+            Err(Error::AmbiguousDFA(..))
+        ));
+        //dfa.to_dot_file("dfa.dot").unwrap();
+    }
+
     proptest! {
         #[test]
-        fn accepts_arb_expr_input_from_regex((expr, arena, input) in arb_expr_match(Rc::new(TERMINALS.iter().map(|s| ustr(s)).collect()), Rc::new(NONTERMINALS.iter().map(|s| ustr(s)).collect()), 10, 3)) {
-            // println!("{:?}", expr);
-            // println!("{:?}", input);
+        fn accepts_arb_expr_input_from_regex((expr, arena, input) in arb_expr_match(3, 3, Rc::new(TERMINALS.iter().map(|s| ustr(s)).collect()), Rc::new(NONTERMINALS.iter().map(|s| ustr(s)).collect()))) {
+            //println!("{:?}", expr);
+            //println!("{:?}", arena);
+            //println!("{:?}", input);
             let specs = UstrMap::default();
             let regex = Regex::from_expr(expr, &arena.borrow(), &specs).unwrap();
-            let dfa = DFA::from_regex(&regex, DFAInterner::default());
+            //dbg!(&regex.input_from_position);
+            prop_assume!(matches!(regex.ensure_ambiguous_inputs_tail_only(Shell::Bash), Ok(())));
+            prop_assume!(matches!(regex.check_clashing_variants(), Ok(())));
+            let dfa = DFA::from_regex(regex, DFAInternPool::default());
+            prop_assume!(dfa.check_ambiguity_best_effort().is_ok());
             let input: Vec<&str> = input.iter().map(|s| s.as_str()).collect();
             prop_assert!(dfa.accepts(&input, Shell::Bash)?);
         }
 
         #[test]
-        fn minimized_dfa_equivalent_to_input_one((expr, arena, input) in arb_expr_match(Rc::new(TERMINALS.iter().map(|s| ustr(s)).collect()), Rc::new(NONTERMINALS.iter().map(|s| ustr(s)).collect()), 10, 3)) {
+        fn minimized_dfa_equivalent_to_input_one((expr, arena, input) in arb_expr_match(10, 3, Rc::new(TERMINALS.iter().map(|s| ustr(s)).collect()), Rc::new(NONTERMINALS.iter().map(|s| ustr(s)).collect()))) {
             println!("{:?}", expr);
             println!("{:?}", input);
             let specs = UstrMap::default();
             let regex = Regex::from_expr(expr, &arena.borrow(), &specs).unwrap();
-            let dfa = DFA::from_regex(&regex, DFAInterner::default());
+            prop_assume!(matches!(regex.ensure_ambiguous_inputs_tail_only(Shell::Bash), Ok(())));
+            prop_assume!(matches!(regex.check_clashing_variants(), Ok(())));
+            let dfa = DFA::from_regex(regex, DFAInternPool::default());
+            prop_assume!(dfa.check_ambiguity_best_effort().is_ok());
             let input: Vec<&str> = input.iter().map(|s| s.as_str()).collect();
             prop_assert!(dfa.accepts(&input, Shell::Bash)?);
             let minimal_dfa = dfa.minimize();
@@ -1368,115 +1695,34 @@ mod tests {
         let f = Input::literal("f");
         let e = Input::literal("e");
         let i = Input::literal("i");
+        let input_symbols = vec![f.clone(), e.clone(), i.clone()];
+        let f_id = 0;
+        let e_id = 1;
+        let i_id = 2;
         let dfa = {
             let starting_state = 0;
-            let mut transitions: IndexMap<StateId, IndexMap<Input, StateId>> = Default::default();
-            transitions.entry(0).or_default().insert(f.clone(), 1);
-            transitions.entry(1).or_default().insert(e.clone(), 2);
-            transitions.entry(1).or_default().insert(i.clone(), 4);
-            transitions.entry(2).or_default().insert(e.clone(), 3);
-            transitions
-                .entry(4)
-                .or_default()
-                .insert(Input::literal("e"), 5);
+            let mut transitions: IndexMap<StateId, IndexMap<Position, StateId>> =
+                Default::default();
+            transitions.entry(0).or_default().insert(f_id, 1);
+            transitions.entry(1).or_default().insert(e_id, 2);
+            transitions.entry(1).or_default().insert(i_id, 4);
+            transitions.entry(2).or_default().insert(e_id, 3);
+            transitions.entry(4).or_default().insert(e_id, 5);
             let accepting_states = RoaringBitmap::from_iter([3, 5]);
-            let input_symbols = Rc::new(IndexSet::from_iter([f.clone(), e.clone(), i.clone()]));
             DFA {
                 starting_state,
                 transitions,
                 accepting_states,
-                input_symbols,
-                subdfa_interner: DFAInterner::default(),
+                input_from_position: input_symbols,
+                subdfas: DFAInternPool::default(),
             }
         };
         let minimized = dfa.minimize();
         assert_eq!(minimized.starting_state, 0);
         assert_eq!(minimized.accepting_states, RoaringBitmap::from_iter([3]));
-        assert!(minimized.has_transition(0, f, 1));
-        assert!(minimized.has_transition(1, e.clone(), 2));
-        assert!(minimized.has_transition(1, i, 2));
-        assert!(minimized.has_transition(2, e, 3));
-    }
-
-    #[test]
-    fn minimization_fails() {
-        let mut arena: Vec<Expr> = Default::default();
-        let term_baz_id = alloc(&mut arena, Expr::term("--baz"));
-        let nonterm_file1_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let alt1_id = alloc(&mut arena, Alternative(vec![term_baz_id, nonterm_file1_id]));
-        let many1_1_id = alloc(&mut arena, Many1(alt1_id));
-        let many1_2_id = alloc(&mut arena, Many1(many1_1_id));
-        let nonterm_file2_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let seq1_id = alloc(&mut arena, Sequence(vec![many1_2_id, nonterm_file2_id]));
-        let opt1_id = alloc(&mut arena, Optional(seq1_id));
-        let nonterm_file3_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let term_foo_id = alloc(&mut arena, Expr::term("foo"));
-        let seq2_id = alloc(&mut arena, Sequence(vec![nonterm_file3_id, term_foo_id]));
-        let seq3_id = alloc(&mut arena, Sequence(vec![opt1_id, seq2_id]));
-        let term_quux_id = alloc(&mut arena, Expr::term("--quux"));
-        let alt2_id = alloc(&mut arena, Alternative(vec![term_quux_id, seq3_id]));
-        let many1_3_id = alloc(&mut arena, Many1(alt2_id));
-        let nonterm_file4_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let expr = alloc(&mut arena, Alternative(vec![many1_3_id, nonterm_file4_id]));
-        let input = ["--quux", "--baz", "anything", "anything", "foo"];
-        let specs = UstrMap::default();
-        let regex = Regex::from_expr(expr, &arena, &specs).unwrap();
-        let dfa = DFA::from_regex(&regex, DFAInterner::default());
-        assert!(dfa.accepts(&input, Shell::Bash).unwrap());
-        let minimal_dfa = dfa.minimize();
-        assert!(minimal_dfa.accepts(&input, Shell::Bash).unwrap());
-    }
-
-    #[test]
-    fn minimization_counterexample1() {
-        let mut arena: Vec<Expr> = Default::default();
-        let nonterm_file1_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let nonterm_file2_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let seq_id = alloc(
-            &mut arena,
-            Sequence(vec![nonterm_file1_id, nonterm_file2_id]),
-        );
-        let many1_id = alloc(&mut arena, Many1(seq_id));
-        let nonterm_file3_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let expr = alloc(&mut arena, Alternative(vec![many1_id, nonterm_file3_id]));
-        let input = [
-            "anything", "anything", "anything", "anything", "anything", "anything",
-        ];
-        let specs = UstrMap::default();
-        let regex = Regex::from_expr(expr, &arena, &specs).unwrap();
-        let dfa = DFA::from_regex(&regex, DFAInterner::default());
-        assert!(dfa.accepts(&input, Shell::Bash).unwrap());
-        let minimal_dfa = dfa.minimize();
-        assert!(minimal_dfa.accepts(&input, Shell::Bash).unwrap());
-    }
-
-    #[test]
-    fn minimization_counterexample2() {
-        let mut arena: Vec<Expr> = Default::default();
-        let term_baz1_id = alloc(&mut arena, Expr::term("--baz"));
-        let many1_1_id = alloc(&mut arena, Many1(term_baz1_id));
-        let many1_2_id = alloc(&mut arena, Many1(many1_1_id));
-        let nonterm_file1_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let alt1_id = alloc(&mut arena, Alternative(vec![many1_2_id, nonterm_file1_id]));
-        let term_baz2_id = alloc(&mut arena, Expr::term("--baz"));
-        let seq1_id = alloc(&mut arena, Sequence(vec![alt1_id, term_baz2_id]));
-
-        let nonterm_file2_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let nonterm_file3_id = alloc(&mut arena, Expr::nontermref("FILE"));
-        let alt2_id = alloc(
-            &mut arena,
-            Alternative(vec![nonterm_file2_id, nonterm_file3_id]),
-        );
-        let many1_3_id = alloc(&mut arena, Many1(alt2_id));
-
-        let expr = alloc(&mut arena, Sequence(vec![seq1_id, many1_3_id]));
-        let input = ["anything", "--baz", "anything", "anything"];
-
-        let specs = UstrMap::default();
-        let regex = Regex::from_expr(expr, &arena, &specs).unwrap();
-        let dfa = DFA::from_regex(&regex, DFAInterner::default());
-        assert!(dfa.accepts(&input, Shell::Bash).unwrap());
-        let minimal_dfa = dfa.minimize();
-        assert!(minimal_dfa.accepts(&input, Shell::Bash).unwrap());
+        assert!(minimized.has_transition(0, f_id, 1));
+        assert!(minimized.has_transition(1, e_id, 2));
+        assert!(minimized.has_transition(1, i_id, 2));
+        assert!(minimized.has_transition(2, e_id, 3));
     }
 }
diff --git a/src/fish.rs b/src/fish.rs
index da07ce6..f9f3890 100644
--- a/src/fish.rs
+++ b/src/fish.rs
@@ -1,7 +1,7 @@
 use std::io::Write;
 
 use crate::dfa::DFA;
-use crate::grammar::{CmdRegexDecl, Shell, Specialization};
+use crate::grammar::{CmdRegex, Shell, Specialization};
 use crate::regex::Input;
 use crate::{Result, StateId};
 use hashbrown::HashMap;
@@ -476,18 +476,18 @@ pub fn write_subword_fn<W: Write>(
     let mut fallback_nontails: Vec<HashMap<StateId, Vec<(usize, usize)>>> = Default::default();
     fallback_nontails.resize_with(max_fallback_level + 1, Default::default);
 
-    for (from, input, _) in dfa.iter_transitions() {
-        match input {
+    for (from, input_id, _) in dfa.iter_transitions() {
+        match dfa.get_input(input_id).clone() {
             Input::Literal {
                 literal: lit,
-                description: descr,
+                description,
                 fallback_level,
                 ..
             } => {
                 let literal_id = *literal_id_from_input_description
-                    .get(&(*lit, (*descr).unwrap_or("".into())))
+                    .get(&(lit, description.unwrap_or("".into())))
                     .unwrap();
-                fallback_literals[*fallback_level]
+                fallback_literals[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(literal_id);
@@ -498,8 +498,8 @@ pub fn write_subword_fn<W: Write>(
                 fallback_level,
                 ..
             } => {
-                let command_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let command_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(command_id);
@@ -507,16 +507,16 @@ pub fn write_subword_fn<W: Write>(
             Input::Command {
                 cmd,
                 regex:
-                    Some(CmdRegexDecl {
+                    Some(CmdRegex {
                         fish: Some(fish_regex),
                         ..
                     }),
                 fallback_level,
                 ..
             } => {
-                let cmd_id = id_from_cmd.get_index_of(cmd).unwrap();
-                let regex_id = id_from_regex.get_index_of(fish_regex).unwrap();
-                fallback_nontails[*fallback_level]
+                let cmd_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                let regex_id = id_from_regex.get_index_of(&fish_regex).unwrap();
+                fallback_nontails[fallback_level]
                     .entry(from)
                     .or_default()
                     .push((cmd_id, regex_id));
@@ -529,8 +529,8 @@ pub fn write_subword_fn<W: Write>(
                 fallback_level,
                 ..
             } => {
-                let specialized_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let specialized_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(specialized_id);
@@ -821,7 +821,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
             }
             Input::Command { cmd, regex, .. } => {
                 id_from_cmd.insert(*cmd);
-                if let Some(CmdRegexDecl {
+                if let Some(CmdRegex {
                     fish: Some(fish_regex),
                     ..
                 }) = regex
@@ -832,7 +832,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
             Input::Subword {
                 subdfa: subdfaid, ..
             } => {
-                let subdfa = dfa.subdfa_interner.lookup(*subdfaid);
+                let subdfa = dfa.subdfas.lookup(*subdfaid);
                 for input in subdfa.iter_inputs() {
                     match input {
                         Input::Nonterminal {
@@ -846,7 +846,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
                         }
                         Input::Command { cmd, regex, .. } => {
                             id_from_cmd.insert(*cmd);
-                            if let Some(CmdRegexDecl {
+                            if let Some(CmdRegex {
                                 fish: Some(fish_regex),
                                 ..
                             }) = regex
@@ -899,7 +899,7 @@ end
         writeln!(buffer)?;
     }
     for (dfaid, id) in &id_from_dfa {
-        let dfa = dfa.subdfa_interner.lookup(*dfaid);
+        let dfa = dfa.subdfas.lookup(*dfaid);
         write_subword_fn(buffer, command, *id, dfa, &id_from_cmd, &id_from_regex)?;
         writeln!(buffer)?;
         writeln!(buffer)?;
@@ -934,7 +934,7 @@ end
     let literal_id_from_input_description = write_lookup_tables(buffer, dfa, &id_from_regex)?;
 
     for state in dfa.get_all_states() {
-        let subword_transitions = dfa.get_subword_transitions_from(state.try_into().unwrap());
+        let subword_transitions = dfa.get_subword_transitions_from(state);
         if subword_transitions.is_empty() {
             continue;
         }
@@ -1047,18 +1047,18 @@ end
     let mut fallback_nontails: Vec<HashMap<StateId, Vec<(usize, usize)>>> = Default::default();
     fallback_nontails.resize_with(max_fallback_level + 1, Default::default);
 
-    for (from, input, _) in dfa.iter_transitions() {
-        match input {
+    for (from, input_id, _) in dfa.iter_transitions() {
+        match dfa.get_input(input_id).clone() {
             Input::Literal {
                 literal: lit,
-                description: descr,
+                description,
                 fallback_level,
                 ..
             } => {
                 let literal_id = *literal_id_from_input_description
-                    .get(&(*lit, (*descr).unwrap_or("".into())))
+                    .get(&(lit, description.unwrap_or("".into())))
                     .unwrap();
-                fallback_literals[*fallback_level]
+                fallback_literals[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(literal_id);
@@ -1068,8 +1068,8 @@ end
                 fallback_level,
                 ..
             } => {
-                let subword_id = *id_from_dfa.get(dfa).unwrap();
-                fallback_subwords[*fallback_level]
+                let subword_id = *id_from_dfa.get(&dfa).unwrap();
+                fallback_subwords[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(subword_id);
@@ -1080,8 +1080,8 @@ end
                 fallback_level,
                 ..
             } => {
-                let command_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let command_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(command_id);
@@ -1089,16 +1089,16 @@ end
             Input::Command {
                 cmd,
                 regex:
-                    Some(CmdRegexDecl {
+                    Some(CmdRegex {
                         fish: Some(fish_regex),
                         ..
                     }),
                 fallback_level,
                 ..
             } => {
-                let cmd_id = id_from_cmd.get_index_of(cmd).unwrap();
-                let regex_id = id_from_regex.get_index_of(fish_regex).unwrap();
-                fallback_nontails[*fallback_level]
+                let cmd_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                let regex_id = id_from_regex.get_index_of(&fish_regex).unwrap();
+                fallback_nontails[fallback_level]
                     .entry(from)
                     .or_default()
                     .push((cmd_id, regex_id));
@@ -1111,8 +1111,8 @@ end
                 fallback_level,
                 ..
             } => {
-                let specialized_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let specialized_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(specialized_id);
diff --git a/src/grammar.rs b/src/grammar.rs
index 73bf4f7..5af11a6 100644
--- a/src/grammar.rs
+++ b/src/grammar.rs
@@ -1,6 +1,6 @@
-use std::debug_assert;
+use std::{debug_assert, io::Write};
 
-use hashbrown::HashMap;
+use indexmap::IndexSet;
 use nom::{
     Finish, IResult, Parser,
     branch::alt,
@@ -18,33 +18,21 @@ use ustr::{Ustr, UstrMap, UstrSet, ustr};
 use crate::{dfa::DFA, regex::Regex};
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-pub struct DFAId(u32);
-
-impl From<u32> for DFAId {
-    fn from(value: u32) -> Self {
-        Self(value)
-    }
-}
+pub struct DFAId(usize);
 
 #[derive(Debug, Clone, Default)]
-pub struct DFAInterner {
-    map: HashMap<DFA, u32>,
-    vec: Vec<DFA>,
+pub struct DFAInternPool {
+    store: IndexSet<DFA>,
 }
 
-impl DFAInterner {
-    pub fn intern(&mut self, val: DFA) -> DFAId {
-        if let Some(&idx) = self.map.get(&val) {
-            return DFAId(idx);
-        }
-        let idx = self.map.len() as u32;
-        self.map.insert(val.clone(), idx);
-        self.vec.push(val);
-        DFAId::from(idx)
+impl DFAInternPool {
+    pub fn intern(&mut self, value: DFA) -> DFAId {
+        let (id, _) = self.store.insert_full(value);
+        DFAId(id)
     }
 
-    pub fn lookup(&self, idx: DFAId) -> &DFA {
-        &self.vec[idx.0 as usize]
+    pub fn lookup(&self, id: DFAId) -> &DFA {
+        self.store.get_index(id.0).unwrap()
     }
 }
 
@@ -66,14 +54,36 @@ impl std::fmt::Debug for SubwordCompilationPhase {
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-pub struct ExprId(usize);
+pub struct ExprId(pub usize);
+
+impl std::fmt::Display for ExprId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl std::ops::Index<ExprId> for Vec<Expr> {
+    type Output = Expr;
 
-impl ExprId {
-    pub fn to_index(&self) -> usize {
-        self.0
+    fn index(&self, index: ExprId) -> &Self::Output {
+        &self[index.0]
     }
 }
 
+impl std::ops::Index<ExprId> for [Expr] {
+    type Output = Expr;
+
+    fn index(&self, index: ExprId) -> &Self::Output {
+        &self[index.0]
+    }
+}
+
+pub fn alloc(arena: &mut Vec<Expr>, elem: Expr) -> ExprId {
+    let id = arena.len();
+    arena.push(elem);
+    ExprId(id)
+}
+
 #[derive(Clone)]
 pub enum Expr {
     // `--help`
@@ -96,7 +106,7 @@ pub enum Expr {
     // `{{{ ls }}}@bash"foo"@fish"bar"`
     Command {
         cmd: Ustr,
-        regex: Option<CmdRegexDecl>,
+        regex: Option<CmdRegex>,
         fallback: usize,
         span: Option<HumanSpan>,
     },
@@ -134,7 +144,7 @@ pub enum Expr {
 
 // Invariant: At least one field must be Some(_)
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct CmdRegexDecl {
+pub struct CmdRegex {
     pub bash: Option<Ustr>,
     pub fish: Option<Ustr>,
     pub zsh: Option<Ustr>,
@@ -147,7 +157,7 @@ pub enum Shell {
     Zsh,
 }
 
-impl CmdRegexDecl {
+impl CmdRegex {
     pub fn matches_anything(&self, shell: Shell) -> bool {
         match shell {
             Shell::Bash => self.bash.is_none(),
@@ -169,162 +179,149 @@ impl std::fmt::Debug for Expr {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
             Self::Subword {
-                phase: subword,
-                fallback: level,
-                ..
-            } => f.write_fmt(format_args!(r#"Subword({subword:?}, {level})"#)),
+                phase, fallback, ..
+            } => f.write_fmt(format_args!(r#"Subword({phase:?}, {fallback})"#)),
             Expr::Terminal {
                 term,
                 descr: Some(descr),
-                fallback: level,
+                fallback,
                 ..
             } => f.write_fmt(format_args!(
-                r#"Terminal(ustr(\"{term}\"), Some(ustr(\"{}\"))), {level})"#,
+                r#"Terminal {{ term: ustr("{term}"), descr: Some(ustr("{}"))), fallback: {fallback}, span: None }}"#,
                 descr
             )),
             Expr::Terminal {
                 term,
                 descr: None,
-                fallback: level,
+                fallback,
                 ..
-            } => f.write_fmt(format_args!(r#"Terminal(ustr(\"{term}\"), None, {level})"#)),
+            } => f.write_fmt(format_args!(
+                r#"Terminal {{ term: ustr("{term}"), descr: None, fallback: {fallback}, span: None }}"#
+            )),
             Expr::NontermRef {
                 nonterm,
-                fallback: level,
-                span: _,
-            } => f.write_fmt(format_args!(r#"Nonterminal(ustr(\"{nonterm}\"), {level})"#)),
+                fallback,
+                ..
+            } => f.write_fmt(format_args!(
+                r#"NontermRef {{ nonterm: ustr("{nonterm}"), fallback: {fallback}, span: None }}"#
+            )),
             Self::Command {
                 cmd,
                 regex,
-                fallback: level,
+                fallback,
                 span,
             } => f.write_fmt(format_args!(
-                r#"Command(ustr({cmd:?}), {regex:?}, {level}, {span:?})"#
+                r#"Command(ustr({cmd:?}), {regex:?}, {fallback}, {span:?})"#
             )),
-            Self::Sequence(arg0) => f.write_fmt(format_args!(r#"Sequence(vec!{:?})"#, arg0)),
-            Self::Alternative(arg0) => f.write_fmt(format_args!(r#"Alternative(vec!{:?})"#, arg0)),
-            Self::Optional(arg0) => f.write_fmt(format_args!(r#"Optional({:?})"#, arg0)),
-            Self::Many1(arg0) => f.write_fmt(format_args!(r#"Many1({:?})"#, arg0)),
-            Self::DistributiveDescription { child: expr, descr } => f.write_fmt(format_args!(
-                r#"DistributiveDescription({expr:?}, {descr:?})"#
+            Self::Sequence(children) => {
+                f.write_fmt(format_args!(r#"Sequence(vec!{:?})"#, children))
+            }
+            Self::Alternative(children) => {
+                f.write_fmt(format_args!(r#"Alternative(vec!{:?})"#, children))
+            }
+            Self::Optional(child) => f.write_fmt(format_args!(r#"Optional({:?})"#, child)),
+            Self::Many1(child) => f.write_fmt(format_args!(r#"Many1({:?})"#, child)),
+            Self::DistributiveDescription { child, descr } => f.write_fmt(format_args!(
+                r#"DistributiveDescription({child:?}, {descr:?})"#
             )),
-            Self::Fallback(arg0) => f.write_fmt(format_args!(r#"Fallback(vec!{:?})"#, arg0)),
+            Self::Fallback(children) => {
+                f.write_fmt(format_args!(r#"Fallback(vec!{:?})"#, children))
+            }
         }
     }
 }
 
-pub fn alloc<T>(arena: &mut Vec<T>, elem: T) -> ExprId {
-    let id = arena.len();
-    arena.push(elem);
-    ExprId(id)
-}
-
-fn railroad_node_from_expr(arena: &[Expr], expr_id: ExprId) -> Box<dyn railroad::Node> {
-    match &arena[expr_id.to_index()] {
-        Expr::Subword { phase: subword, .. } => {
-            let expr = match subword {
-                SubwordCompilationPhase::Expr(expr) => *expr,
-                SubwordCompilationPhase::DFA(_) => unreachable!(),
-            };
-            let mut seq: Box<railroad::Sequence<Box<dyn railroad::Node>>> = Default::default();
-            seq.push(Box::new(railroad::SimpleStart));
-            seq.push(railroad_node_from_expr(arena, expr));
-            seq.push(Box::new(railroad::SimpleEnd));
-            seq
+fn do_expr_to_dot<W: Write>(
+    output: &mut W,
+    expr_id: ExprId,
+    arena: &[Expr],
+) -> std::result::Result<(), std::io::Error> {
+    match arena[expr_id].clone() {
+        Expr::Terminal { term, .. } => {
+            writeln!(output, r#"  _{expr_id}[label="\"{term}\""];"#)?;
         }
-        Expr::Terminal { term, .. } => Box::new(railroad::Terminal::new(term.as_str().to_string())),
         Expr::NontermRef { nonterm, .. } => {
-            Box::new(railroad::NonTerminal::new(nonterm.as_str().to_string()))
+            writeln!(output, r#"  _{expr_id}[label="<{nonterm}>"];"#)?;
         }
-        Expr::Command { cmd, .. } => Box::new(railroad::Comment::new(cmd.as_str().to_string())),
-        Expr::Sequence(subexprs) => {
-            let subnodes: Vec<Box<dyn railroad::Node>> = subexprs
-                .iter()
-                .map(|e| railroad_node_from_expr(arena, *e))
-                .collect();
-            Box::new(railroad::Sequence::new(subnodes))
+        Expr::Command { cmd, .. } => {
+            writeln!(output, r#"  _{expr_id}[label="{cmd}"];"#)?;
         }
-        Expr::Alternative(subexprs) => {
-            let subnodes: Vec<Box<dyn railroad::Node>> = subexprs
-                .iter()
-                .map(|e| railroad_node_from_expr(arena, *e))
-                .collect();
-            Box::new(railroad::Choice::new(subnodes))
+        Expr::Sequence(children) => {
+            writeln!(output, r#"  _{expr_id}[label="Sequence"];"#)?;
+            for child in &children {
+                writeln!(output, r#"  _{expr_id} -> _{child};"#)?;
+            }
+            for child in children {
+                do_expr_to_dot(output, child, arena)?;
+            }
         }
-        Expr::Optional(subexpr) => Box::new(railroad::Optional::new(railroad_node_from_expr(
-            arena, *subexpr,
-        ))),
-        Expr::Many1(subexpr) => {
-            let subnode = railroad_node_from_expr(arena, *subexpr);
-            Box::new(railroad::Repeat::new(subnode, Box::new(railroad::Empty)))
+        Expr::Alternative(children) => {
+            writeln!(output, r#"  _{expr_id}[label="Alternative"];"#)?;
+            for child in &children {
+                writeln!(output, r#"  _{expr_id} -> _{child};"#)?;
+            }
+            for child in children {
+                do_expr_to_dot(output, child, arena)?;
+            }
         }
-        Expr::DistributiveDescription {
-            child: subexpr,
-            descr: description,
-        } => {
-            let inner = railroad_node_from_expr(arena, *subexpr);
-            let label = railroad::Comment::new(description.to_string());
-            Box::new(railroad::LabeledBox::new(inner, label))
+        Expr::Fallback(children) => {
+            writeln!(output, r#"  _{expr_id}[label="Fallback"];"#)?;
+            for child in &children {
+                writeln!(output, r#"  _{expr_id} -> _{child};"#)?;
+            }
+            for child in children {
+                do_expr_to_dot(output, child, arena)?;
+            }
         }
-        Expr::Fallback(subexprs) => {
-            let subnodes: Vec<Box<dyn railroad::Node>> = subexprs
-                .iter()
-                .map(|e| railroad_node_from_expr(arena, *e))
-                .collect();
-            Box::new(railroad::Choice::new(subnodes))
+        Expr::Optional(child) => {
+            writeln!(output, r#"  _{expr_id}[label="Optional"];"#)?;
+            writeln!(output, r#"  _{expr_id} -> _{child};"#)?;
+            do_expr_to_dot(output, child, arena)?;
         }
+        Expr::Many1(child) => {
+            writeln!(output, r#"  _{expr_id}[label="Many1"];"#)?;
+            writeln!(output, r#"  _{expr_id} -> _{child};"#)?;
+            do_expr_to_dot(output, child, arena)?;
+        }
+        Expr::DistributiveDescription { child, .. } => {
+            writeln!(output, r#"  _{expr_id}[label="DistributiveDescription"];"#)?;
+            writeln!(output, r#"  _{expr_id} -> _{child};"#)?;
+        }
+        Expr::Subword {
+            phase: SubwordCompilationPhase::Expr(child),
+            ..
+        } => {
+            writeln!(output, "  subgraph _{expr_id} {{")?;
+            do_expr_to_dot(output, child, arena)?;
+            writeln!(output, "  }}")?;
+        }
+        Expr::Subword {
+            phase: SubwordCompilationPhase::DFA(..),
+            ..
+        } => unreachable!(),
     }
+    Ok(())
 }
 
-pub fn to_railroad_diagram<W: std::io::Write>(
-    grammar: &Grammar,
+pub fn expr_to_dot<W: Write>(
     output: &mut W,
+    root_id: ExprId,
+    arena: &[Expr],
 ) -> std::result::Result<(), std::io::Error> {
-    let mut vertical: railroad::VerticalGrid<Box<dyn railroad::Node>> = Default::default();
-
-    for stmt in &grammar.statements {
-        let node: Box<dyn railroad::Node> = match stmt {
-            Statement::CallVariant { head, expr } => {
-                let mut seq: Box<railroad::Sequence<Box<dyn railroad::Node>>> = Default::default();
-                seq.push(Box::new(railroad::Start));
-                seq.push(Box::new(railroad::Terminal::new(head.to_string())));
-                seq.push(railroad_node_from_expr(&grammar.arena, *expr));
-                seq.push(Box::new(railroad::End));
-                seq
-            }
-            Statement::NonterminalDefinition {
-                symbol,
-                shell,
-                expr,
-            } => {
-                let inner = railroad_node_from_expr(&grammar.arena, *expr);
-                let label = if let Some(shell) = shell {
-                    format!("{}@{}", symbol, shell)
-                } else {
-                    symbol.to_string()
-                };
-                let label = railroad::Comment::new(label);
-                Box::new(railroad::LabeledBox::new(inner, label))
-            }
-        };
-        vertical.push(node);
-    }
-
-    let mut dia = railroad::Diagram::new(vertical);
-    dia.add_element(
-        railroad::svg::Element::new("style")
-            .set("type", "text/css")
-            .text(railroad::DEFAULT_CSS),
-    );
-    dia.write(output)
+    writeln!(output, "digraph rx {{")?;
+    do_expr_to_dot(output, root_id, arena)?;
+    writeln!(output, "}}")?;
+    Ok(())
 }
 
-pub fn to_railroad_diagram_file<P: AsRef<std::path::Path>>(
-    grammar: &Grammar,
+#[allow(dead_code)]
+pub fn expr_to_dot_file<P: AsRef<std::path::Path>>(
     path: P,
+    root_id: ExprId,
+    arena: &[Expr],
 ) -> std::result::Result<(), std::io::Error> {
     let mut file = std::fs::File::create(path)?;
-    to_railroad_diagram(grammar, &mut file)?;
+    expr_to_dot(&mut file, root_id, arena)?;
     Ok(())
 }
 
@@ -456,8 +453,8 @@ fn description(input: Span) -> IResult<Span, String> {
     Ok((input, descr))
 }
 
-fn terminal_opt_description_expr<'a, 's>(
-    arena: &'a mut Vec<Expr>,
+fn terminal_opt_description_expr<'s>(
+    arena: &mut Vec<Expr>,
     input: Span<'s>,
 ) -> IResult<Span<'s>, ExprId> {
     let (after, term) = terminal(input)?;
@@ -479,7 +476,7 @@ fn nonterm(input: Span) -> IResult<Span, Span> {
     Ok((input, name))
 }
 
-fn nonterm_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
+fn nonterm_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (after, nonterm) = context("nonterminal", nonterm)(input)?;
     let diagnostic_span = HumanSpan::new(input, after);
     let e = Expr::NontermRef {
@@ -498,7 +495,7 @@ fn triple_bracket_command(input: Span) -> IResult<Span, Span> {
     Ok((input, Span::new(cmd.into_fragment().trim())))
 }
 
-fn command_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
+fn command_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (after, cmd) = triple_bracket_command(input)?;
     let command_span = HumanSpan::new(input, after);
     let e = Expr::Command {
@@ -522,8 +519,8 @@ fn at_shell_regex(input: Span) -> IResult<Span, (String, String)> {
     Ok((input, (shell, regex)))
 }
 
-fn cmd_regex_decl(mut input: Span) -> IResult<Span, CmdRegexDecl> {
-    let mut spec = CmdRegexDecl::default();
+fn cmd_regex_decl(mut input: Span) -> IResult<Span, CmdRegex> {
+    let mut spec = CmdRegex::default();
     while let Ok((rest, (shell, regex))) = at_shell_regex(input) {
         match shell.as_ref() {
             "bash" => spec.bash = Some(ustr(regex.as_ref())),
@@ -534,7 +531,7 @@ fn cmd_regex_decl(mut input: Span) -> IResult<Span, CmdRegexDecl> {
         input = rest;
     }
 
-    if let CmdRegexDecl {
+    if let CmdRegex {
         bash: None,
         fish: None,
         zsh: None,
@@ -546,8 +543,8 @@ fn cmd_regex_decl(mut input: Span) -> IResult<Span, CmdRegexDecl> {
     Ok((input, spec))
 }
 
-fn nontail_command_expr<'a, 's>(
-    arena: &'a mut Vec<Expr>,
+fn nontail_command_expr<'s>(
+    arena: &mut Vec<Expr>,
     mut input: Span<'s>,
 ) -> IResult<Span<'s>, ExprId> {
     let (after, cmd) = triple_bracket_command(input)?;
@@ -564,7 +561,7 @@ fn nontail_command_expr<'a, 's>(
     Ok((input, id))
 }
 
-fn optional_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
+fn optional_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (input, _) = char('[')(input)?;
     let (input, _) = multiblanks0(input)?;
     let (input, expr) = expr(arena, input)?;
@@ -574,10 +571,7 @@ fn optional_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<S
     Ok((input, id))
 }
 
-fn parenthesized_expr<'a, 's>(
-    arena: &'a mut Vec<Expr>,
-    input: Span<'s>,
-) -> IResult<Span<'s>, ExprId> {
+fn parenthesized_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (input, _) = char('(')(input)?;
     let (input, _) = multiblanks0(input)?;
     let (input, e) = expr(arena, input)?;
@@ -592,7 +586,7 @@ fn many1_tag(input: Span) -> IResult<Span, ()> {
     Ok((input, ()))
 }
 
-fn unary_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
+fn unary_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (input, e) = 'alt: {
         if let Ok((input, e)) = nonterm_expr(arena, input) {
             break 'alt (input, e);
@@ -626,10 +620,7 @@ fn unary_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span
     Ok((input, e))
 }
 
-fn subword_sequence_expr<'a, 's>(
-    arena: &'a mut Vec<Expr>,
-    input: Span<'s>,
-) -> IResult<Span<'s>, ExprId> {
+fn subword_sequence_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (mut after, left) = unary_expr(arena, input)?;
     let mut factors: Vec<ExprId> = vec![left];
     while let Ok((rest, right)) = unary_expr(arena, after) {
@@ -656,8 +647,8 @@ fn subword_sequence_expr<'a, 's>(
     Ok((after, result))
 }
 
-fn subword_sequence_expr_opt_description<'a, 's>(
-    arena: &'a mut Vec<Expr>,
+fn subword_sequence_expr_opt_description<'s>(
+    arena: &mut Vec<Expr>,
     input: Span<'s>,
 ) -> IResult<Span<'s>, ExprId> {
     let (input, expr_id) = subword_sequence_expr(arena, input)?;
@@ -675,7 +666,7 @@ fn subword_sequence_expr_opt_description<'a, 's>(
     Ok((input, result))
 }
 
-fn sequence_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
+fn sequence_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (mut input, left) = subword_sequence_expr_opt_description(arena, input)?;
     let mut factors: Vec<ExprId> = vec![left];
     while let Ok((rest, right)) = preceded(multiblanks1, |i| {
@@ -693,10 +684,7 @@ fn sequence_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<S
     Ok((input, result))
 }
 
-fn do_alternative_expr<'a, 's>(
-    arena: &'a mut Vec<Expr>,
-    input: Span<'s>,
-) -> IResult<Span<'s>, ExprId> {
+fn do_alternative_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (input, _) = multiblanks0(input)?;
     let (input, _) = char('|')(input)?;
     let (input, _) = multiblanks0(input)?;
@@ -704,10 +692,7 @@ fn do_alternative_expr<'a, 's>(
     Ok((input, right))
 }
 
-fn alternative_expr<'a, 's>(
-    arena: &'a mut Vec<Expr>,
-    input: Span<'s>,
-) -> IResult<Span<'s>, ExprId> {
+fn alternative_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (mut input, left) = sequence_expr(arena, input)?;
     let mut elems: Vec<ExprId> = vec![left];
     while let Ok((rest, right)) = do_alternative_expr(arena, input) {
@@ -722,10 +707,7 @@ fn alternative_expr<'a, 's>(
     Ok((input, result))
 }
 
-fn do_fallback_expr<'a, 's>(
-    arena: &'a mut Vec<Expr>,
-    input: Span<'s>,
-) -> IResult<Span<'s>, ExprId> {
+fn do_fallback_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (input, _) = multiblanks0(input)?;
     let (input, _) = tag("||")(input)?;
     let (input, _) = multiblanks0(input)?;
@@ -733,7 +715,7 @@ fn do_fallback_expr<'a, 's>(
     Ok((input, right))
 }
 
-fn fallback_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
+fn fallback_expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     let (mut input, left) = alternative_expr(arena, input)?;
     let mut fallbacks: Vec<ExprId> = vec![left];
     while let Ok((rest, right)) = do_fallback_expr(arena, input) {
@@ -748,7 +730,7 @@ fn fallback_expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<S
     Ok((input, result))
 }
 
-fn expr<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
+fn expr<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, ExprId> {
     fallback_expr(arena, input)
 }
 
@@ -765,7 +747,7 @@ pub enum Statement {
     },
 }
 
-fn call_variant<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, Statement> {
+fn call_variant<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, Statement> {
     let (input, name) = terminal(input)?;
     let (input, _) = multiblanks1(input)?;
     let (input, expr) = expr(arena, input)?;
@@ -799,8 +781,8 @@ fn nonterm_def(input: Span) -> IResult<Span, (Span, Option<Span>)> {
     fail(input)
 }
 
-fn nonterm_def_statement<'a, 's>(
-    arena: &'a mut Vec<Expr>,
+fn nonterm_def_statement<'s>(
+    arena: &mut Vec<Expr>,
     input: Span<'s>,
 ) -> IResult<Span<'s>, Statement> {
     let (input, (name, shell)) = nonterm_def(input)?;
@@ -820,7 +802,7 @@ fn nonterm_def_statement<'a, 's>(
     Ok((input, stmt))
 }
 
-fn statement<'a, 's>(arena: &'a mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, Statement> {
+fn statement<'s>(arena: &mut Vec<Expr>, input: Span<'s>) -> IResult<Span<'s>, Statement> {
     let (input, stmt) = 'alt: {
         if let Ok((input, stmt)) = call_variant(arena, input) {
             break 'alt (input, stmt);
@@ -855,7 +837,7 @@ pub struct ValidGrammar {
     pub specializations: UstrMap<Specialization>,
     pub undefined_nonterminals: UstrSet,
     pub unused_nonterminals: UstrSet,
-    pub subdfa_interner: DFAInterner,
+    pub subdfas: DFAInternPool,
 }
 
 fn make_specializations_map(
@@ -873,7 +855,7 @@ fn make_specializations_map(
             Statement::NonterminalDefinition { shell: None, .. } => continue,
             Statement::CallVariant { .. } => continue,
         };
-        let command = match &arena[expr.to_index()] {
+        let command = match &arena[*expr] {
             Expr::Command { cmd, .. } => cmd,
             _ => return Err(Error::NonCommandSpecialization(name, Some(*shell))),
         };
@@ -917,7 +899,7 @@ fn make_specializations_map(
         let Some(spec) = specializations.get_mut(name) else {
             continue;
         };
-        let Expr::Command { cmd: command, .. } = &arena[expr.to_index()] else {
+        let Expr::Command { cmd: command, .. } = &arena[*expr] else {
             return Err(Error::NonCommandSpecialization(*name, None));
         };
         if spec.generic.is_some() {
@@ -1010,7 +992,7 @@ fn make_specializations_map(
 // Used in subword mode, when we know there won't be any sub-DFAs needed, just one big one.
 // Substitutes Expr::Subword with Expr to make AST simpler to process.
 fn flatten_expr(arena: &mut Vec<Expr>, expr_id: ExprId) -> ExprId {
-    match arena[expr_id.to_index()].clone() {
+    match arena[expr_id].clone() {
         Expr::Terminal { .. } | Expr::NontermRef { .. } | Expr::Command { .. } => expr_id,
         Expr::Subword { phase: child, .. } => {
             let child = match child {
@@ -1087,9 +1069,9 @@ fn compile_subword_exprs(
     expr_id: ExprId,
     specs: &UstrMap<Specialization>,
     shell: Shell,
-    subdfa_interner: &mut DFAInterner,
+    subdfas: &mut DFAInternPool,
 ) -> Result<ExprId> {
-    let retval = match arena[expr_id.to_index()].clone() {
+    let retval = match arena[expr_id].clone() {
         Expr::Subword {
             phase: subword_expr,
             fallback,
@@ -1103,9 +1085,9 @@ fn compile_subword_exprs(
             let regex = Regex::from_expr(subword_expr, arena, specs).unwrap();
             regex.ensure_ambiguous_inputs_tail_only_subword(shell)?;
             regex.check_clashing_variants()?;
-            let dfa = DFA::from_regex(&regex, DFAInterner::default());
+            let dfa = DFA::from_regex_strict(regex, DFAInternPool::default())?;
             let dfa = dfa.minimize();
-            let subdfaid = subdfa_interner.intern(dfa);
+            let subdfaid = subdfas.intern(dfa);
             alloc(
                 arena,
                 Expr::Subword {
@@ -1119,7 +1101,7 @@ fn compile_subword_exprs(
         Expr::Sequence(children) => {
             let new_children: Vec<ExprId> = children
                 .iter()
-                .map(|e| compile_subword_exprs(arena, *e, specs, shell, subdfa_interner))
+                .map(|e| compile_subword_exprs(arena, *e, specs, shell, subdfas))
                 .collect::<Result<_>>()?;
             if children == new_children {
                 expr_id
@@ -1130,7 +1112,7 @@ fn compile_subword_exprs(
         Expr::Alternative(children) => {
             let new_children: Vec<ExprId> = children
                 .iter()
-                .map(|e| compile_subword_exprs(arena, *e, specs, shell, subdfa_interner))
+                .map(|e| compile_subword_exprs(arena, *e, specs, shell, subdfas))
                 .collect::<Result<_>>()?;
             if children == new_children {
                 expr_id
@@ -1139,7 +1121,7 @@ fn compile_subword_exprs(
             }
         }
         Expr::Optional(child) => {
-            let new_child = compile_subword_exprs(arena, child, specs, shell, subdfa_interner)?;
+            let new_child = compile_subword_exprs(arena, child, specs, shell, subdfas)?;
             if child == new_child {
                 expr_id
             } else {
@@ -1147,7 +1129,7 @@ fn compile_subword_exprs(
             }
         }
         Expr::Many1(child) => {
-            let new_child = compile_subword_exprs(arena, child, specs, shell, subdfa_interner)?;
+            let new_child = compile_subword_exprs(arena, child, specs, shell, subdfas)?;
             if child == new_child {
                 expr_id
             } else {
@@ -1160,7 +1142,7 @@ fn compile_subword_exprs(
         Expr::Fallback(children) => {
             let new_children: Vec<ExprId> = children
                 .iter()
-                .map(|e| compile_subword_exprs(arena, *e, specs, shell, subdfa_interner))
+                .map(|e| compile_subword_exprs(arena, *e, specs, shell, subdfas))
                 .collect::<Result<_>>()?;
             if children == new_children {
                 expr_id
@@ -1178,7 +1160,7 @@ fn do_distribute_descriptions(
     expr_id: ExprId,
     description: &mut Option<Ustr>,
 ) -> ExprId {
-    match arena[expr_id.to_index()].clone() {
+    match arena[expr_id].clone() {
         Expr::DistributiveDescription { child, descr } => {
             let new_child = do_distribute_descriptions(arena, child, &mut Some(descr));
             if child == new_child { child } else { new_child }
@@ -1286,15 +1268,10 @@ fn do_propagate_fallback_levels(
     expr_id: ExprId,
     fallback_level: usize,
 ) -> ExprId {
-    match arena[expr_id.to_index()].clone() {
-        Expr::Terminal {
-            fallback: level, ..
-        } if level == fallback_level => expr_id,
+    match arena[expr_id].clone() {
+        Expr::Terminal { fallback, .. } if fallback == fallback_level => expr_id,
         Expr::Terminal {
-            term,
-            descr,
-            fallback: _,
-            span,
+            term, descr, span, ..
         } => alloc(
             arena,
             Expr::Terminal {
@@ -1486,13 +1463,13 @@ impl ValidGrammar {
             nonterms
         };
 
-        let mut subdfa_interner = DFAInterner::default();
+        let mut subdfas = DFAInternPool::default();
         let expr = compile_subword_exprs(
             &mut grammar.arena,
             expr,
             &specializations,
             shell,
-            &mut subdfa_interner,
+            &mut subdfas,
         )?;
 
         let g = ValidGrammar {
@@ -1502,14 +1479,14 @@ impl ValidGrammar {
             undefined_nonterminals,
             specializations,
             unused_nonterminals,
-            subdfa_interner,
+            subdfas,
         };
         Ok(g)
     }
 }
 
 fn expr_get_head(arena: &[Expr], expr_id: ExprId) -> ExprId {
-    match &arena[expr_id.to_index()] {
+    match &arena[expr_id] {
         Expr::Terminal { .. }
         | Expr::NontermRef { .. }
         | Expr::Command { .. }
@@ -1526,7 +1503,7 @@ fn expr_get_head(arena: &[Expr], expr_id: ExprId) -> ExprId {
 }
 
 fn expr_get_tail(arena: &[Expr], expr_id: ExprId) -> ExprId {
-    match &arena[expr_id.to_index()] {
+    match &arena[expr_id] {
         Expr::Terminal { .. }
         | Expr::NontermRef { .. }
         | Expr::Command { .. }
@@ -1561,7 +1538,7 @@ fn do_check_subword_spaces(
     nonterm_expn_trace: &mut Vec<HumanSpan>,
     within_subword: bool,
 ) -> Result<()> {
-    match &arena[expr_id.to_index()] {
+    match &arena[expr_id] {
         Expr::Sequence(children) if within_subword => {
             for child in children {
                 do_check_subword_spaces(
@@ -1584,7 +1561,7 @@ fn do_check_subword_spaces(
                     Expr::Terminal {
                         span: right_span, ..
                     },
-                ) = (&arena[left_tail.to_index()], &arena[right_head.to_index()])
+                ) = (&arena[left_tail], &arena[right_head])
                 {
                     return Err(Error::SubwordSpaces(
                         left_span.to_owned(),
@@ -1616,7 +1593,7 @@ fn do_check_subword_spaces(
                 nonterm_expn_trace.push(span);
             }
             do_check_subword_spaces(arena, *expn, nonterms, nonterm_expn_trace, within_subword)?;
-            if let Some(_) = *span {
+            if span.is_some() {
                 nonterm_expn_trace.pop();
             }
             Ok(())
@@ -1675,7 +1652,7 @@ fn resolve_nonterminals(
     specializations: &UstrMap<Specialization>,
     unused_nonterminals: &mut UstrSet,
 ) -> ExprId {
-    match arena[expr_id.to_index()].clone() {
+    match arena[expr_id].clone() {
         Expr::Terminal { .. } | Expr::Command { .. } => expr_id,
         Expr::Subword {
             phase: SubwordCompilationPhase::Expr(child),
@@ -1781,7 +1758,7 @@ fn resolve_nonterminals(
 }
 
 fn do_get_expression_nonterminals(arena: &[Expr], expr_id: ExprId, deps: &mut UstrSet) {
-    match &arena[expr_id.to_index()] {
+    match &arena[expr_id] {
         Expr::Terminal { .. } | Expr::Command { .. } => {}
         Expr::Subword { phase, .. } => {
             let subexpr = match phase {
@@ -1921,7 +1898,6 @@ fn get_nonterminals_resolution_order(
             .unwrap_or(true)
     });
 
-    log::debug!("nonterminals expansion order: {:?}", result);
     Ok(result)
 }
 
@@ -2007,11 +1983,11 @@ pub mod tests {
 
     // Extensional equality.  Ignores spans
     fn teq(left: ExprId, right: ExprId, arena: &[Expr]) -> bool {
-        if left.to_index() == right.to_index() {
+        if left == right {
             return true;
         }
 
-        match (&arena[left.to_index()], &arena[right.to_index()]) {
+        match (&arena[left], &arena[right]) {
             (
                 Expr::Terminal {
                     term: l,
@@ -2220,7 +2196,7 @@ pub mod tests {
         let (s, e) = command_expr(&mut arena, Span::new(INPUT)).unwrap();
         assert!(s.is_empty());
         assert!(
-            matches!(arena[e.to_index()], Command { cmd: s, regex: None, fallback: 0, .. } if s == "rustup toolchain list | cut -d' ' -f1")
+            matches!(arena[e], Command { cmd: s, regex: None, fallback: 0, .. } if s == "rustup toolchain list | cut -d' ' -f1")
         );
     }
 
@@ -2234,7 +2210,7 @@ pub mod tests {
             &mut arena,
             Command {
                 cmd: ustr("foo"),
-                regex: Some(CmdRegexDecl {
+                regex: Some(CmdRegex {
                     bash: Some(ustr("bar")),
                     fish: None,
                     zsh: None,
@@ -3323,7 +3299,7 @@ ls <FILE>;
             &mut arena,
             Command {
                 cmd: ustr("echo foo"),
-                regex: Some(CmdRegexDecl {
+                regex: Some(CmdRegex {
                     bash: Some(ustr("bar")),
                     fish: Some(ustr("baz")),
                     zsh: Some(ustr("quux")),
diff --git a/src/lib.rs b/src/lib.rs
index 178bd36..190596c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -35,7 +35,10 @@ pub enum Error {
     NonCommandSpecialization(Ustr, Option<Ustr>),
 
     #[error("Ambiguity in matching: {:?} {:?}", .0, .1)]
-    AmbiguousMatchable(Input, Input),
+    AmbiguousMatchable(Box<Input>, Box<Input>),
+
+    #[error("Ambiguous DFA: {:?} {:?}", .0, .1)]
+    AmbiguousDFA(Box<[Input]>, Box<[Input]>),
 
     #[error("Clashing variants: {:?} {:?}", .0, .1)]
     ClashingVariants(Option<HumanSpan>, Option<HumanSpan>),
@@ -55,4 +58,4 @@ pub enum Error {
 
 pub type Result<T> = std::result::Result<T, Error>;
 
-pub type StateId = u16;
+pub type StateId = u32;
diff --git a/src/main.rs b/src/main.rs
index 85db8ca..2fa7d2b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -6,11 +6,11 @@ use std::process::exit;
 use anyhow::{Context, bail};
 use clap::Parser;
 
-use complgen::grammar::{Grammar, HumanSpan, Shell, ValidGrammar, to_railroad_diagram_file};
+use complgen::grammar::{Grammar, HumanSpan, Shell, ValidGrammar};
 
 use complgen::Error;
 use complgen::dfa::DFA;
-use complgen::regex::Regex;
+use complgen::regex::{Regex, diagnostic_display_input};
 
 #[derive(clap::Parser)]
 struct Cli {
@@ -36,17 +36,17 @@ struct Cli {
 
     #[clap(
         long,
-        help = "Write DFA in GraphViz .dot format",
-        name = "DFA_DOT_PATH"
+        help = "Write regex in GraphViz .dot format",
+        name = "REGEX_DOT_PATH"
     )]
-    dfa: Option<String>,
+    regex: Option<String>,
 
     #[clap(
         long,
-        help = "Write .usage grammar as a railroad diagram (SVG)",
-        name = "RAILROAD_SVG_PATH"
+        help = "Write DFA in GraphViz .dot format",
+        name = "DFA_DOT_PATH"
     )]
-    railroad: Option<String>,
+    dfa: Option<String>,
 }
 
 fn get_file_or_stdin(path: &str) -> anyhow::Result<Box<dyn Read>> {
@@ -59,7 +59,7 @@ fn get_file_or_stdin(path: &str) -> anyhow::Result<Box<dyn Read>> {
 }
 
 fn handle_parse_error(input: &str) -> anyhow::Result<Grammar> {
-    match Grammar::parse(&input) {
+    match Grammar::parse(input) {
         Ok(g) => Ok(g),
         Err(e) => {
             eprintln!("{}", e.to_string());
@@ -68,12 +68,11 @@ fn handle_parse_error(input: &str) -> anyhow::Result<Grammar> {
     }
 }
 
-fn handle_validation_error(e: Error, input: &str) -> anyhow::Result<ValidGrammar> {
+fn handle_validation_error(e: Error, input: &str, command: &str) -> anyhow::Result<()> {
     match e {
         Error::VaryingCommandNames(cmds) => {
             let joined = itertools::join(cmds.into_iter().map(|c| format!("{c}")), ", ");
             eprintln!("Multiple commands specified: {joined}");
-            exit(1);
         }
         Error::SubwordSpaces(left, right, trace) => {
             let HumanSpan {
@@ -127,7 +126,6 @@ fn handle_validation_error(e: Error, input: &str) -> anyhow::Result<ValidGrammar
                 );
                 eprintln!("{}:{}:{}", line_start, start, e.to_string());
             }
-            exit(1);
         }
         Error::AmbiguousMatchable(first, second) => {
             let Some(HumanSpan {
@@ -163,7 +161,24 @@ fn handle_validation_error(e: Error, input: &str) -> anyhow::Result<ValidGrammar
                 "",
             );
             eprintln!("{}:{}:{}", right_line_start, right_start, error.to_string());
-            exit(1);
+        }
+        Error::AmbiguousDFA(path, ambiguous_inputs) => {
+            let joined_path = {
+                let mut buf = String::new();
+                for (i, inp) in path.iter().enumerate() {
+                    diagnostic_display_input(&mut buf, &inp)?;
+                    if i < path.len() - 1 {
+                        buf.push_str(" ");
+                    }
+                }
+                buf
+            };
+            eprintln!("Ambiguity:");
+            for input in ambiguous_inputs {
+                let mut buffer = String::new();
+                diagnostic_display_input(&mut buffer, &input)?;
+                eprintln!("  {command} {joined_path} {buffer}");
+            }
         }
         Error::ClashingVariants(first, second) => {
             let Some(HumanSpan {
@@ -199,13 +214,12 @@ fn handle_validation_error(e: Error, input: &str) -> anyhow::Result<ValidGrammar
                 "",
             );
             eprintln!("{}:{}:{}", right_line_start, right_start, error.to_string());
-            exit(1);
         }
         e => {
-            eprintln!("{}", e.to_string());
-            exit(1);
+            eprintln!("{}", e);
         }
     }
+    exit(1);
 }
 
 fn get_file_or_stdout(path: &str) -> anyhow::Result<Box<dyn Write>> {
@@ -223,7 +237,7 @@ fn aot(args: &Cli) -> anyhow::Result<()> {
     };
 
     let input = {
-        let mut usage_file = get_file_or_stdin(&usage_file_path)?;
+        let mut usage_file = get_file_or_stdin(usage_file_path)?;
         let mut input = String::default();
         usage_file
             .read_to_string(&mut input)
@@ -233,51 +247,49 @@ fn aot(args: &Cli) -> anyhow::Result<()> {
 
     let grammar = handle_parse_error(&input)?;
 
-    if let Some(railroad_svg_path) = &args.railroad {
-        to_railroad_diagram_file(&grammar, railroad_svg_path).context(railroad_svg_path.clone())?;
-    }
-
     let (shell, path) = match (&args.bash, &args.fish, &args.zsh) {
         (Some(path), None, None) => (Shell::Bash, path),
         (None, Some(path), None) => (Shell::Fish, path),
         (None, None, Some(path)) => (Shell::Zsh, path),
 
-        _ => todo!(),
+        _ => {
+            eprintln!("Please specify at least one of: --bash, --fish, --zsh");
+            exit(1);
+        }
     };
 
     let validated = match ValidGrammar::from_grammar(grammar, shell) {
         Ok(validated) => validated,
-        Err(e) => {
-            handle_validation_error(e, &input)?;
-            return Ok(());
-        }
+        Err(e) => return handle_validation_error(e, &input, "dummy"),
     };
 
     if !validated.undefined_nonterminals.is_empty() {
-        let joined = itertools::join(validated.undefined_nonterminals, " ");
+        let joined = itertools::join(&validated.undefined_nonterminals, " ");
         eprintln!("warning: undefined nonterminal(s): {}", joined);
     }
 
     if !validated.unused_nonterminals.is_empty() {
-        let joined = itertools::join(validated.unused_nonterminals, " ");
+        let joined = itertools::join(&validated.unused_nonterminals, " ");
         eprintln!("warning: unused nonterminal(s): {}", joined);
     }
 
-    log::debug!("Grammar -> Regex");
-    let regex = Regex::from_expr(validated.expr, &validated.arena, &validated.specializations)?;
-
-    if let Err(e) = regex.ensure_ambiguous_inputs_tail_only(shell) {
-        handle_validation_error(e, &input)?;
-    }
+    let regex = match Regex::from_valid_grammar(&validated, shell) {
+        Ok(regex) => regex,
+        Err(e) => return handle_validation_error(e, &input, &validated.command),
+    };
 
-    if let Err(e) = regex.check_clashing_variants() {
-        handle_validation_error(e, &input)?;
+    if let Some(regex_dot_file_path) = &args.regex {
+        let mut dot_file = get_file_or_stdout(regex_dot_file_path)?;
+        regex
+            .to_dot(&mut dot_file)
+            .context(regex_dot_file_path.clone())?;
     }
 
-    log::debug!("Regex -> DFA");
-    let dfa = DFA::from_regex(&regex, validated.subdfa_interner);
+    let dfa = match DFA::from_regex_strict(regex, validated.subdfas) {
+        Ok(dfa) => dfa,
+        Err(e) => return handle_validation_error(e, &input, &validated.command),
+    };
 
-    log::debug!("Minimizing DFA");
     let dfa = dfa.minimize();
 
     if let Some(dot_file_path) = &args.dfa {
@@ -324,7 +336,6 @@ fn scrape() -> anyhow::Result<()> {
 }
 
 fn main() -> anyhow::Result<()> {
-    env_logger::init();
     let args = Cli::parse();
 
     if args.version {
diff --git a/src/regex.rs b/src/regex.rs
index ea599d3..c04bf39 100644
--- a/src/regex.rs
+++ b/src/regex.rs
@@ -1,14 +1,16 @@
-use crate::{Error, Result};
+use crate::{Error, Result, grammar::ValidGrammar};
 use hashbrown::HashSet;
-use indexmap::IndexSet;
-use std::collections::{BTreeMap, BTreeSet};
-use std::rc::Rc;
+use indexmap::IndexMap;
+use std::{
+    collections::{BTreeMap, BTreeSet},
+    io::Write,
+};
 
 use roaring::RoaringBitmap;
 use ustr::{Ustr, UstrMap};
 
 use crate::grammar::{
-    CmdRegexDecl, DFAId, Expr, ExprId, HumanSpan, Shell, Specialization, SubwordCompilationPhase,
+    CmdRegex, DFAId, Expr, ExprId, HumanSpan, Shell, Specialization, SubwordCompilationPhase,
 };
 
 pub type Position = u32;
@@ -34,7 +36,7 @@ pub enum Input {
     },
     Command {
         cmd: Ustr,
-        regex: Option<CmdRegexDecl>,
+        regex: Option<CmdRegex>,
         fallback_level: usize,
         span: Option<HumanSpan>,
     },
@@ -84,22 +86,47 @@ impl Input {
     }
 }
 
-impl std::fmt::Display for Input {
+pub fn diagnostic_display_input<W: std::fmt::Write>(w: &mut W, input: &Input) -> crate::Result<()> {
+    match input {
+        Input::Literal { literal, .. } => write!(w, r#"{literal}"#)?,
+        Input::Nonterminal { nonterm, .. } => write!(w, r#"<{nonterm}>"#)?,
+        Input::Command { cmd, .. } => write!(w, r#"{{{{{{ {cmd} }}}}}}"#)?,
+        Input::Subword { .. } => unreachable!(),
+    }
+    Ok(())
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct RegexNodeId(usize);
+
+impl std::fmt::Display for RegexNodeId {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Self::Subword {
-                subdfa: subword, ..
-            } => write!(f, r#"{subword:?}"#),
-            Self::Literal { literal, .. } => write!(f, r#"{literal}"#),
-            Self::Nonterminal {
-                nonterm: nonterminal,
-                ..
-            } => write!(f, r#"<{nonterminal}>"#),
-            Self::Command { cmd: command, .. } => write!(f, r#"{{{{{{ {command} }}}}}}"#),
-        }
+        write!(f, "{}", self.0)
+    }
+}
+
+impl std::ops::Index<RegexNodeId> for Vec<RegexNode> {
+    type Output = RegexNode;
+
+    fn index(&self, index: RegexNodeId) -> &Self::Output {
+        &self[index.0]
     }
 }
 
+impl std::ops::Index<RegexNodeId> for [RegexNode] {
+    type Output = RegexNode;
+
+    fn index(&self, index: RegexNodeId) -> &Self::Output {
+        &self[index.0]
+    }
+}
+
+fn alloc(arena: &mut Vec<RegexNode>, elem: RegexNode) -> RegexNodeId {
+    let id = arena.len();
+    arena.push(elem);
+    RegexNodeId(id)
+}
+
 #[derive(Clone, PartialEq)]
 pub enum RegexNode {
     Epsilon,
@@ -107,9 +134,9 @@ pub enum RegexNode {
     Terminal(Ustr, usize, Position), // terminal, fallback level, position
     Nonterminal(Position),
     Command(Ustr, Position),
-    Cat(usize, usize),
-    Or(Box<[usize]>, bool), // is fallback
-    Star(usize),
+    Cat(RegexNodeId, RegexNodeId),
+    Or(Box<[RegexNodeId]>, bool), // is fallback
+    Star(RegexNodeId),
     EndMarker(Position),
 }
 
@@ -118,22 +145,18 @@ impl std::fmt::Debug for RegexNode {
         match self {
             Self::Subword(position) => f.write_fmt(format_args!(r#"Subword({position})"#)),
             Self::Terminal(term, level, position) => f.write_fmt(format_args!(
-                r#"Terminal({:?}.to_string(), {level}, {position})"#,
-                term
+                r#"Terminal({term:?}.to_string(), {level}, {position})"#
             )),
-            Self::Nonterminal(position) => {
-                f.write_fmt(format_args!(r#"Nonterminal({})"#, position))
+            Self::Nonterminal(position) => f.write_fmt(format_args!(r#"Nonterminal({position})"#)),
+            Self::Command(code, position) => {
+                f.write_fmt(format_args!(r#"Command({code:?}.to_string(), {position})"#))
             }
-            Self::Command(code, position) => f.write_fmt(format_args!(
-                r#"Command({:?}.to_string(), {})"#,
-                code, position
-            )),
-            Self::Cat(left, right) => f.write_fmt(format_args!(r#"Cat({:?}, {:?})"#, left, right)),
-            Self::Or(arg0, is_fallback) => {
-                f.write_fmt(format_args!(r#"Or(vec!{:?}, {is_fallback})"#, arg0))
+            Self::Cat(left, right) => f.write_fmt(format_args!(r#"Cat({left:?}, {right:?})"#)),
+            Self::Or(children, is_fallback) => {
+                f.write_fmt(format_args!(r#"Or(vec!{children:?}, {is_fallback})"#))
             }
-            Self::Star(arg0) => f.write_fmt(format_args!(r#"Star({:?})"#, arg0)),
-            Self::EndMarker(position) => f.write_fmt(format_args!(r#"EndMarker({})"#, position)),
+            Self::Star(child) => f.write_fmt(format_args!(r#"Star({child:?})"#)),
+            Self::EndMarker(position) => f.write_fmt(format_args!(r#"EndMarker({position})"#)),
             Self::Epsilon => f.write_fmt(format_args!(r#"Epsilon"#)),
         }
     }
@@ -305,21 +328,14 @@ impl RegexNode {
     }
 }
 
-fn alloc<T>(arena: &mut Vec<T>, elem: T) -> usize {
-    let id = arena.len();
-    arena.push(elem);
-    id
-}
-
 fn do_from_expr(
     e: ExprId,
     expr_arena: &[Expr],
     specs: &UstrMap<Specialization>,
     arena: &mut Vec<RegexNode>,
-    symbols: &mut IndexSet<Input>,
     input_from_position: &mut Vec<Input>,
-) -> usize {
-    match &expr_arena[e.to_index()] {
+) -> RegexNodeId {
+    match &expr_arena[e] {
         Expr::Terminal {
             term,
             descr: description,
@@ -338,121 +354,88 @@ fn do_from_expr(
                 span: *span,
             };
             input_from_position.push(input.clone());
-            symbols.insert(input);
             alloc(arena, result)
         }
         Expr::Subword {
-            phase: subword,
-            fallback: fallback_level,
+            phase,
+            fallback,
             span,
         } => {
             let result = RegexNode::Subword(Position::try_from(input_from_position.len()).unwrap());
-            let dfa = match subword {
+            let dfa = match phase {
                 SubwordCompilationPhase::DFA(dfa) => dfa,
                 SubwordCompilationPhase::Expr(_) => unreachable!(),
             };
             let input = Input::Subword {
                 subdfa: *dfa,
-                fallback_level: *fallback_level,
+                fallback_level: *fallback,
                 span: *span,
             };
             input_from_position.push(input.clone());
-            symbols.insert(input);
             alloc(arena, result)
         }
         Expr::NontermRef {
-            nonterm: name,
-            fallback: fallback_level,
+            nonterm,
+            fallback,
             span,
         } => {
             let result =
                 RegexNode::Nonterminal(Position::try_from(input_from_position.len()).unwrap());
-            let specialization = specs.get(name);
+            let specialization = specs.get(nonterm);
             let input = Input::Nonterminal {
-                nonterm: *name,
+                nonterm: *nonterm,
                 spec: specialization.copied(),
-                fallback_level: *fallback_level,
+                fallback_level: *fallback,
                 span: *span,
             };
             input_from_position.push(input.clone());
-            symbols.insert(input);
             alloc(arena, result)
         }
         Expr::Command {
-            cmd: code,
-            regex: cmd_regex_decl,
-            fallback: fallback_level,
+            cmd,
+            regex,
+            fallback,
             span,
         } => {
-            let result = RegexNode::Command(
-                *code,
-                Position::try_from(input_from_position.len()).unwrap(),
-            );
+            let result =
+                RegexNode::Command(*cmd, Position::try_from(input_from_position.len()).unwrap());
             let input = Input::Command {
-                cmd: *code,
-                regex: *cmd_regex_decl,
-                fallback_level: *fallback_level,
+                cmd: *cmd,
+                regex: *regex,
+                fallback_level: *fallback,
                 span: *span,
             };
             input_from_position.push(input.clone());
-            symbols.insert(input);
             alloc(arena, result)
         }
         Expr::Sequence(subexprs) => {
-            let mut left_regex_id = do_from_expr(
-                subexprs[0],
-                expr_arena,
-                specs,
-                arena,
-                symbols,
-                input_from_position,
-            );
+            let mut left_regex_id =
+                do_from_expr(subexprs[0], expr_arena, specs, arena, input_from_position);
             for right_expr in &subexprs[1..] {
-                let right_regex_id = do_from_expr(
-                    *right_expr,
-                    expr_arena,
-                    specs,
-                    arena,
-                    symbols,
-                    input_from_position,
-                );
+                let right_regex_id =
+                    do_from_expr(*right_expr, expr_arena, specs, arena, input_from_position);
                 let left_regex = RegexNode::Cat(left_regex_id, right_regex_id);
                 left_regex_id = alloc(arena, left_regex);
             }
             left_regex_id
         }
         Expr::Alternative(subexprs) => {
-            let mut subregexes: Vec<usize> = Default::default();
+            let mut subregexes: Vec<RegexNodeId> = Default::default();
             for e in subexprs {
-                let subregex =
-                    do_from_expr(*e, expr_arena, specs, arena, symbols, input_from_position);
+                let subregex = do_from_expr(*e, expr_arena, specs, arena, input_from_position);
                 subregexes.push(subregex);
             }
             let result = RegexNode::Or(subregexes.into_boxed_slice(), false);
             alloc(arena, result)
         }
         Expr::Optional(subexpr) => {
-            let subregex = do_from_expr(
-                *subexpr,
-                expr_arena,
-                specs,
-                arena,
-                symbols,
-                input_from_position,
-            );
+            let subregex = do_from_expr(*subexpr, expr_arena, specs, arena, input_from_position);
             let epsid = alloc(arena, RegexNode::Epsilon);
             let result = RegexNode::Or(Box::new([subregex, epsid]), false);
             alloc(arena, result)
         }
         Expr::Many1(subexpr) => {
-            let subregex_id = do_from_expr(
-                *subexpr,
-                expr_arena,
-                specs,
-                arena,
-                symbols,
-                input_from_position,
-            );
+            let subregex_id = do_from_expr(*subexpr, expr_arena, specs, arena, input_from_position);
             let star = RegexNode::Star(subregex_id);
             let starid = alloc(arena, star);
             let result = RegexNode::Cat(subregex_id, starid);
@@ -462,10 +445,9 @@ fn do_from_expr(
             "DistributiveDescription Expr type should have been erased before compilation to regex"
         ),
         Expr::Fallback(subexprs) => {
-            let mut subregexes: Vec<usize> = Default::default();
+            let mut subregexes: Vec<RegexNodeId> = Default::default();
             for e in subexprs {
-                let subregex =
-                    do_from_expr(*e, expr_arena, specs, arena, symbols, input_from_position);
+                let subregex = do_from_expr(*e, expr_arena, specs, arena, input_from_position);
                 subregexes.push(subregex);
             }
             let result = RegexNode::Or(subregexes.into_boxed_slice(), true);
@@ -476,8 +458,7 @@ fn do_from_expr(
 
 #[derive(Debug)]
 pub struct Regex {
-    pub root: RegexNode,
-    pub input_symbols: Rc<IndexSet<Input>>,
+    pub root_id: RegexNodeId,
     pub input_from_position: Vec<Input>,
     pub endmarker_position: Position,
     pub arena: Vec<RegexNode>,
@@ -494,6 +475,7 @@ Ambiguous matching arises from:
 fn do_ensure_ambiguous_inputs_tail_only(
     firstpos: &RoaringBitmap,
     followpos: &BTreeMap<Position, RoaringBitmap>,
+    endmarker_position: Position,
     input_from_position: &Vec<Input>,
     shell: Shell,
     visited: &mut RoaringBitmap,
@@ -503,8 +485,9 @@ fn do_ensure_ambiguous_inputs_tail_only(
         return Ok(());
     }
 
-    let inputs: Vec<Input> = unvisited
+    let inputs: Vec<Input> = firstpos
         .iter()
+        .filter(|pos| *pos != endmarker_position)
         .map(|pos| input_from_position[pos as usize].clone())
         .collect();
 
@@ -512,7 +495,7 @@ fn do_ensure_ambiguous_inputs_tail_only(
     for inp in inputs {
         if inp.is_ambiguous(shell) {
             if let Some(prev_inp) = prev_ambiguous {
-                return Err(Error::AmbiguousMatchable(prev_inp, inp));
+                return Err(Error::AmbiguousMatchable(Box::new(prev_inp), Box::new(inp)));
             }
             prev_ambiguous = Some(inp);
         }
@@ -526,6 +509,7 @@ fn do_ensure_ambiguous_inputs_tail_only(
         do_ensure_ambiguous_inputs_tail_only(
             follow,
             followpos,
+            endmarker_position,
             input_from_position,
             shell,
             visited,
@@ -557,11 +541,14 @@ fn do_ensure_ambiguous_inputs_tail_only_subword(
     let mut prev_ambiguous: Option<Input> = None;
     for inp in inputs {
         if let Some(ref prev_inp) = path_prev_ambiguous {
-            return Err(Error::AmbiguousMatchable(prev_inp.clone(), inp));
+            return Err(Error::AmbiguousMatchable(
+                Box::new(prev_inp.clone()),
+                Box::new(inp),
+            ));
         }
 
         if let Some(prev_inp) = prev_ambiguous {
-            return Err(Error::AmbiguousMatchable(prev_inp, inp));
+            return Err(Error::AmbiguousMatchable(Box::new(prev_inp), Box::new(inp)));
         }
         if inp.is_ambiguous(shell) {
             prev_ambiguous = Some(inp);
@@ -643,30 +630,85 @@ fn do_check_clashing_variants(
     Ok(())
 }
 
+fn do_to_dot<W: Write>(
+    output: &mut W,
+    node_id: RegexNodeId,
+    arena: &[RegexNode],
+    input_from_position: &Vec<Input>,
+) -> std::result::Result<(), std::io::Error> {
+    match arena[node_id].clone() {
+        RegexNode::Epsilon => {
+            writeln!(output, r#"  _{node_id}[label="Epsilon"];"#)?;
+        }
+        RegexNode::Subword(pos) => {
+            writeln!(output, r#"  _{node_id}[label="{pos}: Subword"];"#)?;
+        }
+        RegexNode::Terminal(term, _, pos) => {
+            writeln!(output, r#"  _{node_id}[label="{pos}: \"{term}\""];"#)?;
+        }
+        RegexNode::Nonterminal(pos) => {
+            let input = input_from_position[pos as usize].clone();
+            let Input::Nonterminal { nonterm, .. } = input else {
+                unreachable!()
+            };
+            writeln!(output, r#"  _{node_id}[label="{pos}: <{nonterm}>"];"#)?;
+        }
+        RegexNode::Command(cmd, pos) => {
+            writeln!(output, r#"  _{node_id}[label="{pos}: {cmd}"];"#)?;
+        }
+        RegexNode::Cat(lhs, rhs) => {
+            writeln!(
+                output,
+                r#"  _{node_id}[label="Cat"]; _{node_id} -> _{lhs}; _{node_id} -> _{rhs};"#
+            )?;
+            do_to_dot(output, lhs, arena, input_from_position)?;
+            do_to_dot(output, rhs, arena, input_from_position)?;
+        }
+        RegexNode::Or(ors, _) => {
+            writeln!(output, r#"  _{node_id}[label="Or"];"#)?;
+            for child in &ors {
+                writeln!(output, r#"  _{node_id} -> _{child};"#)?;
+            }
+            for child in ors {
+                do_to_dot(output, child, arena, input_from_position)?;
+            }
+        }
+        RegexNode::Star(child) => {
+            writeln!(
+                output,
+                r#"  _{node_id}[label="Star"]; _{node_id} -> _{child};"#
+            )?;
+        }
+        RegexNode::EndMarker(pos) => {
+            writeln!(output, r#"  _{node_id}[label="{pos}: EndMarker"];"#)?;
+        }
+    }
+    Ok(())
+}
+
 impl Regex {
+    pub fn from_valid_grammar(v: &ValidGrammar, shell: Shell) -> Result<Self> {
+        let regex = Self::from_expr(v.expr, &v.arena, &v.specializations)?;
+        regex.ensure_ambiguous_inputs_tail_only(shell)?;
+        regex.check_clashing_variants()?;
+        Ok(regex)
+    }
+
     pub fn from_expr(
         e: ExprId,
         expr_arena: &[Expr],
         specs: &UstrMap<Specialization>,
     ) -> Result<Self> {
-        let mut input_symbols: IndexSet<Input> = Default::default();
         let mut input_from_position: Vec<Input> = Default::default();
         let mut arena: Vec<RegexNode> = Default::default();
-        let regex = do_from_expr(
-            e,
-            expr_arena,
-            specs,
-            &mut arena,
-            &mut input_symbols,
-            &mut input_from_position,
-        );
+        let regex = do_from_expr(e, expr_arena, specs, &mut arena, &mut input_from_position);
         let endmarker_position = input_from_position.len() as Position;
         let endmarkerid = alloc(&mut arena, RegexNode::EndMarker(endmarker_position));
         let root = RegexNode::Cat(regex, endmarkerid);
+        let root_id = alloc(&mut arena, root.clone());
 
         let retval = Self {
-            root,
-            input_symbols: Rc::new(input_symbols),
+            root_id,
             endmarker_position,
             input_from_position,
             arena,
@@ -674,12 +716,20 @@ impl Regex {
         Ok(retval)
     }
 
+    pub fn get_unique_inputs(&self) -> IndexMap<Input, Position> {
+        let mut result: IndexMap<Input, Position> = Default::default();
+        for (id, input) in self.input_from_position.iter().enumerate() {
+            result.entry(input.clone()).or_insert(id as Position);
+        }
+        result
+    }
+
     pub fn ensure_ambiguous_inputs_tail_only(&self, shell: Shell) -> Result<()> {
         let mut visited: RoaringBitmap = Default::default();
-        visited.insert(self.endmarker_position);
         do_ensure_ambiguous_inputs_tail_only(
-            &RoaringBitmap::from_iter(&self.root.firstpos(&self.arena)),
-            &self.root.followpos(&self.arena),
+            &RoaringBitmap::from_iter(&self.firstpos()),
+            &self.followpos(),
+            self.endmarker_position,
             &self.input_from_position,
             shell,
             &mut visited,
@@ -690,8 +740,8 @@ impl Regex {
         let mut visited: RoaringBitmap = Default::default();
         visited.insert(self.endmarker_position);
         do_ensure_ambiguous_inputs_tail_only_subword(
-            &RoaringBitmap::from_iter(&self.root.firstpos(&self.arena)),
-            &self.root.followpos(&self.arena),
+            &RoaringBitmap::from_iter(&self.firstpos()),
+            &self.followpos(),
             &self.input_from_position,
             shell,
             None,
@@ -704,19 +754,40 @@ impl Regex {
         let mut visited: RoaringBitmap = Default::default();
         visited.insert(self.endmarker_position);
         do_check_clashing_variants(
-            &RoaringBitmap::from_iter(&self.root.firstpos(&self.arena)),
-            &self.root.followpos(&self.arena),
+            &RoaringBitmap::from_iter(&self.firstpos()),
+            &self.followpos(),
             &self.input_from_position,
             &mut visited,
         )
     }
 
+    pub fn get_root(&self) -> &RegexNode {
+        &self.arena[self.root_id]
+    }
+
     pub fn firstpos(&self) -> BTreeSet<Position> {
-        self.root.firstpos(&self.arena)
+        self.get_root().firstpos(&self.arena)
     }
 
     pub fn followpos(&self) -> BTreeMap<Position, RoaringBitmap> {
-        self.root.followpos(&self.arena)
+        self.get_root().followpos(&self.arena)
+    }
+
+    pub fn to_dot<W: Write>(&self, output: &mut W) -> std::result::Result<(), std::io::Error> {
+        writeln!(output, "digraph rx {{")?;
+        do_to_dot(output, self.root_id, &self.arena, &self.input_from_position)?;
+        writeln!(output, "}}")?;
+        Ok(())
+    }
+
+    #[allow(dead_code)]
+    pub fn to_dot_file<P: AsRef<std::path::Path>>(
+        &self,
+        path: P,
+    ) -> std::result::Result<(), std::io::Error> {
+        let mut file = std::fs::File::create(path)?;
+        self.to_dot(&mut file)?;
+        Ok(())
     }
 }
 
@@ -726,7 +797,7 @@ mod tests {
     use crate::{Error, Result};
     use ustr::ustr;
 
-    fn make_sample_star_regex(arena: &mut Vec<RegexNode>) -> usize {
+    fn make_sample_star_regex(arena: &mut Vec<RegexNode>) -> RegexNodeId {
         let t1 = alloc(arena, RegexNode::Terminal(ustr("a"), 0, 1));
         let t2 = alloc(arena, RegexNode::Terminal(ustr("b"), 0, 2));
         let or_ = RegexNode::Or(Box::new([t1, t2]), false);
diff --git a/src/zsh.rs b/src/zsh.rs
index 2ad11c3..42ed6f3 100644
--- a/src/zsh.rs
+++ b/src/zsh.rs
@@ -1,7 +1,7 @@
 use std::io::Write;
 
 use crate::dfa::DFA;
-use crate::grammar::{CmdRegexDecl, Shell, Specialization};
+use crate::grammar::{CmdRegex, Shell, Specialization};
 use crate::regex::Input;
 use crate::{Result, StateId};
 use hashbrown::HashMap;
@@ -382,18 +382,18 @@ pub fn write_subword_fn<W: Write>(
     let mut fallback_specialized: Vec<HashMap<StateId, Vec<usize>>> = Default::default();
     fallback_specialized.resize_with(max_fallback_level + 1, Default::default);
 
-    for (from, input, _) in dfa.iter_transitions() {
-        match input {
+    for (from, input_id, _) in dfa.iter_transitions() {
+        match dfa.get_input(input_id).clone() {
             Input::Literal {
                 literal: lit,
-                description: descr,
+                description,
                 fallback_level,
                 ..
             } => {
                 let literal_id = *literal_id_from_input_description
-                    .get(&(*lit, (*descr).unwrap_or("".into())))
+                    .get(&(lit, description.unwrap_or("".into())))
                     .unwrap();
-                fallback_literals[*fallback_level]
+                fallback_literals[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(literal_id);
@@ -404,8 +404,8 @@ pub fn write_subword_fn<W: Write>(
                 fallback_level,
                 ..
             } => {
-                let command_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let command_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(command_id);
@@ -413,16 +413,16 @@ pub fn write_subword_fn<W: Write>(
             Input::Command {
                 cmd,
                 regex:
-                    Some(CmdRegexDecl {
+                    Some(CmdRegex {
                         zsh: Some(zsh_regex),
                         ..
                     }),
                 fallback_level,
                 ..
             } => {
-                let cmd_id = id_from_cmd.get_index_of(cmd).unwrap();
-                let regex_id = id_from_regex.get_index_of(zsh_regex).unwrap();
-                fallback_nontails[*fallback_level]
+                let cmd_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                let regex_id = id_from_regex.get_index_of(&zsh_regex).unwrap();
+                fallback_nontails[fallback_level]
                     .entry(from)
                     .or_default()
                     .push((cmd_id, regex_id));
@@ -432,8 +432,8 @@ pub fn write_subword_fn<W: Write>(
                 fallback_level,
                 ..
             } => {
-                let specialized_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_specialized[*fallback_level]
+                let specialized_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_specialized[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(specialized_id);
@@ -558,7 +558,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
             }
             Input::Command { cmd, regex, .. } => {
                 id_from_cmd.insert(*cmd);
-                if let Some(CmdRegexDecl {
+                if let Some(CmdRegex {
                     zsh: Some(zsh_regex),
                     ..
                 }) = regex
@@ -569,7 +569,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
             Input::Subword {
                 subdfa: subdfaid, ..
             } => {
-                let subdfa = dfa.subdfa_interner.lookup(*subdfaid);
+                let subdfa = dfa.subdfas.lookup(*subdfaid);
                 for input in subdfa.iter_inputs() {
                     match input {
                         Input::Nonterminal {
@@ -580,7 +580,7 @@ pub fn make_id_from_command_map(dfa: &DFA) -> (IndexSet<Ustr>, IndexSet<Ustr>) {
                         }
                         Input::Command { cmd, regex, .. } => {
                             id_from_cmd.insert(*cmd);
-                            if let Some(CmdRegexDecl {
+                            if let Some(CmdRegex {
                                 zsh: Some(zsh_regex),
                                 ..
                             }) = regex
@@ -623,7 +623,7 @@ pub fn write_completion_script<W: Write>(buffer: &mut W, command: &str, dfa: &DF
     if !id_from_dfa.is_empty() {
         write_generic_subword_fn(buffer, command)?;
         for (dfaid, id) in &id_from_dfa {
-            let dfa = dfa.subdfa_interner.lookup(*dfaid);
+            let dfa = dfa.subdfas.lookup(*dfaid);
             write_subword_fn(buffer, command, *id, dfa, &id_from_cmd, &id_from_regex)?;
             writeln!(buffer)?;
         }
@@ -635,7 +635,7 @@ pub fn write_completion_script<W: Write>(buffer: &mut W, command: &str, dfa: &DF
 
     writeln!(buffer, r#"    declare -A subword_transitions=()"#)?;
     for state in dfa.get_all_states() {
-        let subword_transitions = dfa.get_subword_transitions_from(state.try_into().unwrap());
+        let subword_transitions = dfa.get_subword_transitions_from(state);
         if subword_transitions.is_empty() {
             continue;
         }
@@ -762,18 +762,18 @@ pub fn write_completion_script<W: Write>(buffer: &mut W, command: &str, dfa: &DF
     let mut fallback_specialized: Vec<HashMap<StateId, Vec<usize>>> = Default::default();
     fallback_specialized.resize_with(max_fallback_level + 1, Default::default);
 
-    for (from, input, _) in dfa.iter_transitions() {
-        match input {
+    for (from, input_id, _) in dfa.iter_transitions() {
+        match dfa.get_input(input_id).clone() {
             Input::Literal {
                 literal: lit,
-                description: descr,
+                description,
                 fallback_level,
                 ..
             } => {
                 let literal_id = *literal_id_from_input_description
-                    .get(&(*lit, (*descr).unwrap_or("".into())))
+                    .get(&(lit, description.unwrap_or("".into())))
                     .unwrap();
-                fallback_literals[*fallback_level]
+                fallback_literals[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(literal_id);
@@ -783,8 +783,8 @@ pub fn write_completion_script<W: Write>(buffer: &mut W, command: &str, dfa: &DF
                 fallback_level,
                 ..
             } => {
-                let subword_id = *id_from_dfa.get(dfa).unwrap();
-                fallback_subwords[*fallback_level]
+                let subword_id = *id_from_dfa.get(&dfa).unwrap();
+                fallback_subwords[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(subword_id);
@@ -795,8 +795,8 @@ pub fn write_completion_script<W: Write>(buffer: &mut W, command: &str, dfa: &DF
                 fallback_level,
                 ..
             } => {
-                let command_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_commands[*fallback_level]
+                let command_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_commands[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(command_id);
@@ -804,16 +804,16 @@ pub fn write_completion_script<W: Write>(buffer: &mut W, command: &str, dfa: &DF
             Input::Command {
                 cmd,
                 regex:
-                    Some(CmdRegexDecl {
+                    Some(CmdRegex {
                         zsh: Some(zsh_regex),
                         ..
                     }),
                 fallback_level,
                 ..
             } => {
-                let cmd_id = id_from_cmd.get_index_of(cmd).unwrap();
-                let regex_id = id_from_regex.get_index_of(zsh_regex).unwrap();
-                fallback_nontails[*fallback_level]
+                let cmd_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                let regex_id = id_from_regex.get_index_of(&zsh_regex).unwrap();
+                fallback_nontails[fallback_level]
                     .entry(from)
                     .or_default()
                     .push((cmd_id, regex_id));
@@ -823,8 +823,8 @@ pub fn write_completion_script<W: Write>(buffer: &mut W, command: &str, dfa: &DF
                 fallback_level,
                 ..
             } => {
-                let specialized_id = id_from_cmd.get_index_of(cmd).unwrap();
-                fallback_specialized[*fallback_level]
+                let specialized_id = id_from_cmd.get_index_of(&cmd).unwrap();
+                fallback_specialized[fallback_level]
                     .entry(from)
                     .or_default()
                     .push(specialized_id);