diff --git a/TODO.md b/TODO.md
index 414fe6d..47284b0 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,18 +1,4 @@
-将 explicit-substitution 从 lambda 中分离出来
-
-# 有待验证的假设
-
-在 explicit-substitution 中实验，然后开始 cicada。
-
-- 用 `assert-equal` 验证基于 `Exp` 的 definitional 等价关系。
-- 验证基于 `Exp` 的递归函数之间的 definitional 等价关系。
-- 验证基于 `Exp` 的 dependent type 类型检查器。
-- 在实现 explicit-substitution 时避免全局的 `globalFreshen`。
-
-# lang1
-
-[lang1] 支持 `(assert-equal)` 与 `(assert-not-equal)`
-[lang1] 支持直接递归函数与相互递归函数，不能判断等价的地方就不判断。
+rename lang0 to lang
 
 # lang0
 
diff --git a/docs/lang1/README.md b/docs/lang1/README.md
deleted file mode 100644
index fc8f7bf..0000000
--- a/docs/lang1/README.md
+++ /dev/null
@@ -1,14 +0,0 @@
-# Lang1
-
-Interpreter of lambda calculus with explicit substitution.
-
-- The meaning of scheme's `(let)` can be viewed as explicit substitution.
-
-```scheme
-(define name body)
-(define (name arg ...) body)
-(import name ... "./file.scm")
-
-(lambda (name) ret)
-(let ([name exp] ...) body)
-```
diff --git a/docs/lang1/examples/boolean.scm b/docs/lang1/examples/boolean.scm
deleted file mode 100644
index 41a685e..0000000
--- a/docs/lang1/examples/boolean.scm
+++ /dev/null
@@ -1,24 +0,0 @@
-;; Boolean
-
-;; # True and False
-
-(define (true t f) t)
-(define (false t f) f)
-
-;; # Logical connectives
-
-(define (if p t f) (p t f))
-
-(define (and x y) (if x y false))
-(define (or x y) (if x true y))
-(define (not x) (if x false true))
-
-;; ## Tests
-
-(and true false) false
-(or true false) true
-(not true) false
-(not (not true)) true
-
-(lambda (x) (not (not true)))
-(lambda (x) true)
diff --git a/docs/lang1/examples/boolean.scm.out b/docs/lang1/examples/boolean.scm.out
deleted file mode 100644
index 8418ce2..0000000
--- a/docs/lang1/examples/boolean.scm.out
+++ /dev/null
@@ -1,10 +0,0 @@
-(lambda (t f) f)
-(lambda (t f) f)
-(lambda (t f) t)
-(lambda (t f) t)
-(lambda (t f) f)
-(lambda (t f) f)
-(lambda (t f) t)
-(lambda (t f) t)
-(lambda (x t f) t)
-(lambda (x t f) t)
diff --git a/docs/lang1/examples/cons.scm b/docs/lang1/examples/cons.scm
deleted file mode 100644
index e69de29..0000000
diff --git a/docs/lang1/examples/nat-church.scm b/docs/lang1/examples/nat-church.scm
deleted file mode 100644
index 07becfb..0000000
--- a/docs/lang1/examples/nat-church.scm
+++ /dev/null
@@ -1,28 +0,0 @@
-;; Church Encoding of Natural Number
-
-(define zero (lambda (base step) base))
-(define (add1 prev) (lambda (base step) (step (prev base step))))
-(define (iter-Nat n base step) (n base step))
-
-(define one (add1 zero))
-(define two (add1 one))
-(define three (add1 two))
-(define four (add1 three))
-(define five (add1 four))
-(define six (add1 five))
-(define seven (add1 six))
-(define eight (add1 seven))
-(define nine (add1 eight))
-(define ten (add1 nine))
-
-(define (add m n) (iter-Nat m n add1))
-
-(add two five) seven
-(add three three) six
-
-(define (add-rosser m n)
-  (lambda (base step)
-    (iter-Nat m (iter-Nat n base step) step)))
-
-(add-rosser two five) seven
-(add-rosser three three) six
diff --git a/docs/lang1/examples/nat-church.scm.out b/docs/lang1/examples/nat-church.scm.out
deleted file mode 100644
index bb1564c..0000000
--- a/docs/lang1/examples/nat-church.scm.out
+++ /dev/null
@@ -1,8 +0,0 @@
-(lambda (base₆ step₁₁) (step₁₁ (step₁₁ (step₁₁ (step₁₁ (step₁₁ (step₁₁ (step₁₁ base₆))))))))
-(lambda (base₁₂ step₂₃) (step₂₃ (step₂₃ (step₂₃ (step₂₃ (step₂₃ (step₂₃ (step₂₃ base₁₂))))))))
-(lambda (base₂₆ step₅₁) (step₅₁ (step₅₁ (step₅₁ (step₅₁ (step₅₁ (step₅₁ base₂₆)))))))
-(lambda (base₃₀ step₅₉) (step₅₉ (step₅₉ (step₅₉ (step₅₉ (step₅₉ (step₅₉ base₃₀)))))))
-(lambda (base₄₁ step₈₁) (step₈₁ (step₈₁ (step₈₁ (step₈₁ (step₈₁ (step₈₁ (step₈₁ base₄₁))))))))
-(lambda (base₄₇ step₉₃) (step₉₃ (step₉₃ (step₉₃ (step₉₃ (step₉₃ (step₉₃ (step₉₃ base₄₇))))))))
-(lambda (base₆₀ step₁₁₉) (step₁₁₉ (step₁₁₉ (step₁₁₉ (step₁₁₉ (step₁₁₉ (step₁₁₉ base₆₀)))))))
-(lambda (base₆₄ step₁₂₇) (step₁₂₇ (step₁₂₇ (step₁₂₇ (step₁₂₇ (step₁₂₇ (step₁₂₇ base₆₄)))))))
diff --git a/docs/lang1/tests/compose.scm b/docs/lang1/tests/compose.scm
deleted file mode 100644
index 3e0f839..0000000
--- a/docs/lang1/tests/compose.scm
+++ /dev/null
@@ -1,3 +0,0 @@
-(define (id x) x)
-
-(define (compose f g x) (f (g x)))
diff --git a/docs/lang1/tests/import.scm b/docs/lang1/tests/import.scm
deleted file mode 100644
index e64f198..0000000
--- a/docs/lang1/tests/import.scm
+++ /dev/null
@@ -1,16 +0,0 @@
-(import id compose (rename compose c) "./compose.scm")
-
-;; (assert-equal
-;;   (compose
-;;    (compose id id)
-;;    (compose id id))
-;;   (c (c id id) (c id id))
-;;   id)
-
-(compose
- (compose id id)
- (compose id id))
-
-(c (c id id) (c id id))
-
-id
diff --git a/docs/lang1/tests/import.scm.out b/docs/lang1/tests/import.scm.out
deleted file mode 100644
index 2fff2c7..0000000
--- a/docs/lang1/tests/import.scm.out
+++ /dev/null
@@ -1,3 +0,0 @@
-(lambda (x₄) x₄)
-(lambda (x₁₀) x₁₀)
-(lambda (x) x)
diff --git a/docs/lang1/tests/invalid-name.error.scm b/docs/lang1/tests/invalid-name.error.scm
deleted file mode 100644
index c61f4d5..0000000
--- a/docs/lang1/tests/invalid-name.error.scm
+++ /dev/null
@@ -1 +0,0 @@
-(lambda (x₀) x₀)
diff --git a/docs/lang1/tests/invalid-name.error.scm.err b/docs/lang1/tests/invalid-name.error.scm.err
deleted file mode 100644
index b0af613..0000000
--- a/docs/lang1/tests/invalid-name.error.scm.err
+++ /dev/null
@@ -1,5 +0,0 @@
-[matchExp] A name should not include subscripts: x₀
-
- 1 |(lambda (x₀) x₀)
- 2 |
-
diff --git a/docs/lang1/tests/let.scm b/docs/lang1/tests/let.scm
deleted file mode 100644
index a295302..0000000
--- a/docs/lang1/tests/let.scm
+++ /dev/null
@@ -1,2 +0,0 @@
-(let ([id (lambda (x) x)])
-  (id id))
diff --git a/docs/lang1/tests/let.scm.out b/docs/lang1/tests/let.scm.out
deleted file mode 100644
index ca37804..0000000
--- a/docs/lang1/tests/let.scm.out
+++ /dev/null
@@ -1 +0,0 @@
-(lambda (x) x)
diff --git a/package.json b/package.json
index 5eb2f70..e16f11f 100644
--- a/package.json
+++ b/package.json
@@ -15,13 +15,10 @@
     "build": "tsc",
     "build:watch": "tsc --watch",
     "test:node": "node --test",
-    "test:lang0:tests": "test-runner snapshot './bin/lambda.js lang0' 'docs/lang0/**/*.scm' --exclude 'docs/lang0/**/*.error.scm'",
-    "test:lang0:tests-error": "test-runner snapshot-error './bin/lambda.js lang0' 'docs/lang0/**/*.error.scm'",
+    "test:lang0:tests": "test-runner snapshot './bin/lambda.js run' 'docs/lang0/**/*.scm' --exclude 'docs/lang0/**/*.error.scm'",
+    "test:lang0:tests-error": "test-runner snapshot-error './bin/lambda.js run' 'docs/lang0/**/*.error.scm'",
     "test:lang0": "npm run test:lang0:tests && npm run test:lang0:tests-error",
-    "test:lang1:tests": "test-runner snapshot './bin/lambda.js lang1' 'docs/lang1/**/*.scm' --exclude 'docs/lang1/**/*.error.scm'",
-    "test:lang1:tests-error": "test-runner snapshot-error './bin/lambda.js lang1' 'docs/lang1/**/*.error.scm'",
-    "test:lang1": "npm run test:lang1:tests && npm run test:lang1:tests-error",
-    "test": "npm run test:node && npm run test:lang0 && npm run test:lang1",
+    "test": "npm run test:node && npm run test:lang0",
     "format": "prettier src docs --write"
   },
   "dependencies": {
diff --git a/src/command-line/commands/Lang1Command.ts b/src/command-line/commands/Lang1Command.ts
deleted file mode 100644
index 24a2a44..0000000
--- a/src/command-line/commands/Lang1Command.ts
+++ /dev/null
@@ -1,57 +0,0 @@
-import { Command, CommandRunner } from "@xieyuheng/command-line"
-import { ty } from "@xieyuheng/ty"
-import fs from "fs"
-import Path from "path"
-import { run } from "../../lang1/run/index.js"
-
-type Args = { file: string }
-type Opts = {}
-
-export class Lang1Command extends Command<Args, Opts> {
-  name = "lang1"
-
-  description = "Run a lang1 file"
-
-  args = { file: ty.string() }
-  opts = {}
-
-  // prettier-ignore
-  help(runner: CommandRunner): string {
-    const { blue } = this.colors
-
-    return [
-      `The ${blue(this.name)} command run a lang1 file.`,
-      ``,
-      blue(`  ${runner.name} ${this.name} <file>`),
-      ``,
-    ].join("\n")
-  }
-
-  async execute(argv: Args & Opts): Promise<void> {
-    const url = createURL(argv["file"])
-
-    try {
-      await run(url)
-    } catch (error) {
-      if (error instanceof Error) {
-        console.error(error.message)
-        process.exit(1)
-      }
-
-      throw error
-    }
-  }
-}
-
-function createURL(path: string): URL {
-  if (ty.url().isValid(path)) {
-    return new URL(path)
-  }
-
-  if (fs.existsSync(path) && fs.lstatSync(path).isFile()) {
-    const fullPath = Path.resolve(path)
-    return new URL(`file:${fullPath}`)
-  }
-
-  throw new Error(`I can not create URL from path: ${path}`)
-}
diff --git a/src/command-line/commands/Lang0Command.ts b/src/command-line/commands/RunCommand.ts
similarity index 86%
rename from src/command-line/commands/Lang0Command.ts
rename to src/command-line/commands/RunCommand.ts
index e12faae..b534f08 100644
--- a/src/command-line/commands/Lang0Command.ts
+++ b/src/command-line/commands/RunCommand.ts
@@ -7,10 +7,10 @@ import { run } from "../../lang0/run/index.js"
 type Args = { file: string }
 type Opts = {}
 
-export class Lang0Command extends Command<Args, Opts> {
-  name = "lang0"
+export class RunCommand extends Command<Args, Opts> {
+  name = "run"
 
-  description = "Run a lang0 file"
+  description = "Run a file"
 
   args = { file: ty.string() }
   opts = {}
@@ -20,7 +20,7 @@ export class Lang0Command extends Command<Args, Opts> {
     const { blue } = this.colors
 
     return [
-      `The ${blue(this.name)} command run a lang0 file.`,
+      `The ${blue(this.name)} command run a file.`,
       ``,
       blue(`  ${runner.name} ${this.name} <file>`),
       ``,
diff --git a/src/command-line/commands/index.ts b/src/command-line/commands/index.ts
index d05523e..310b2a3 100644
--- a/src/command-line/commands/index.ts
+++ b/src/command-line/commands/index.ts
@@ -1,3 +1,2 @@
 export * from "@xieyuheng/command-line/lib/commands/index.js"
-export * from "./Lang0Command.js"
-export * from "./Lang1Command.js"
+export * from "./RunCommand.js"
diff --git a/src/command-line/index.ts b/src/command-line/index.ts
index 1271cf9..0671657 100644
--- a/src/command-line/index.ts
+++ b/src/command-line/index.ts
@@ -7,10 +7,6 @@ import * as Commands from "./commands/index.js"
 export function createCommandRunner(): CommandRunner {
   return new CommandRunners.CommonCommandRunner({
     defaultCommand: new Commands.CommonHelp(),
-    commands: [
-      new Commands.Lang0Command(),
-      new Commands.Lang1Command(),
-      new Commands.CommonHelp(),
-    ],
+    commands: [new Commands.RunCommand(), new Commands.CommonHelp()],
   })
 }
diff --git a/src/lang1/definition/Definition.ts b/src/lang1/definition/Definition.ts
deleted file mode 100644
index cbc1b9e..0000000
--- a/src/lang1/definition/Definition.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-import { type Exp } from "../exp/index.js"
-import { type Mod } from "../mod/index.js"
-
-export type Definition = {
-  mod: Mod
-  name: string
-  exp: Exp
-}
diff --git a/src/lang1/definition/index.ts b/src/lang1/definition/index.ts
deleted file mode 100644
index ff02f98..0000000
--- a/src/lang1/definition/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./Definition.js"
diff --git a/src/lang1/exp/Exp.ts b/src/lang1/exp/Exp.ts
deleted file mode 100644
index fb51bff..0000000
--- a/src/lang1/exp/Exp.ts
+++ /dev/null
@@ -1,81 +0,0 @@
-import { type Substitution } from "../substitution/index.js"
-
-export type Exp = Var | Lazy | Fn | Ap | Let
-
-export type Var = {
-  "@type": "Exp"
-  "@kind": "Var"
-  name: string
-}
-
-export function Var(name: string): Var {
-  return {
-    "@type": "Exp",
-    "@kind": "Var",
-    name,
-  }
-}
-
-export type Lazy = {
-  "@type": "Exp"
-  "@kind": "Lazy"
-  exp: Exp
-  cache?: Exp
-}
-
-export function Lazy(exp: Exp, cache?: Exp): Lazy {
-  return {
-    "@type": "Exp",
-    "@kind": "Lazy",
-    exp,
-    cache,
-  }
-}
-
-export type Fn = {
-  "@type": "Exp"
-  "@kind": "Fn"
-  name: string
-  ret: Exp
-}
-
-export function Fn(name: string, ret: Exp): Fn {
-  return {
-    "@type": "Exp",
-    "@kind": "Fn",
-    name,
-    ret,
-  }
-}
-
-export type Ap = {
-  "@type": "Exp"
-  "@kind": "Ap"
-  target: Exp
-  arg: Exp
-}
-
-export function Ap(target: Exp, arg: Exp): Ap {
-  return {
-    "@type": "Exp",
-    "@kind": "Ap",
-    target,
-    arg,
-  }
-}
-
-export type Let = {
-  "@type": "Exp"
-  "@kind": "Let"
-  substitution: Substitution
-  body: Exp
-}
-
-export function Let(substitution: Substitution, body: Exp): Let {
-  return {
-    "@type": "Exp",
-    "@kind": "Let",
-    substitution,
-    body,
-  }
-}
diff --git a/src/lang1/exp/expFreeNames.ts b/src/lang1/exp/expFreeNames.ts
deleted file mode 100644
index fbc182f..0000000
--- a/src/lang1/exp/expFreeNames.ts
+++ /dev/null
@@ -1,44 +0,0 @@
-import { substitutionBindings } from "../substitution/index.js"
-import { type Exp } from "./index.js"
-
-export function expFreeNames(boundNames: Set<string>, exp: Exp): Set<string> {
-  switch (exp["@kind"]) {
-    case "Var": {
-      return boundNames.has(exp.name) ? new Set() : new Set([exp.name])
-    }
-
-    case "Lazy": {
-      if (exp.cache) {
-        return expFreeNames(boundNames, exp.cache)
-      } else {
-        return expFreeNames(boundNames, exp.exp)
-      }
-    }
-
-    case "Fn": {
-      return expFreeNames(new Set([...boundNames, exp.name]), exp.ret)
-    }
-
-    case "Ap": {
-      return new Set([
-        ...expFreeNames(boundNames, exp.target),
-        ...expFreeNames(boundNames, exp.arg),
-      ])
-    }
-
-    case "Let": {
-      // NOTE All bindings in the substitution are independent.
-      const bindings = substitutionBindings(exp.substitution)
-      const substitutionFreeNames = bindings
-        .map((binding) => Array.from(expFreeNames(boundNames, binding.exp)))
-        .flatMap((names) => names)
-      return new Set([
-        ...substitutionFreeNames,
-        ...expFreeNames(
-          new Set([...boundNames, ...bindings.map((binding) => binding.name)]),
-          exp.body,
-        ),
-      ])
-    }
-  }
-}
diff --git a/src/lang1/exp/index.ts b/src/lang1/exp/index.ts
deleted file mode 100644
index 7b8109a..0000000
--- a/src/lang1/exp/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export * from "./Exp.js"
-export * from "./expFreeNames.js"
diff --git a/src/lang1/format/formatExp.ts b/src/lang1/format/formatExp.ts
deleted file mode 100644
index c05d852..0000000
--- a/src/lang1/format/formatExp.ts
+++ /dev/null
@@ -1,59 +0,0 @@
-import { type Exp } from "../exp/index.js"
-import { substitutionBindings, type Binding } from "../substitution/index.js"
-
-export function formatExp(exp: Exp): string {
-  switch (exp["@kind"]) {
-    case "Var": {
-      return exp.name
-    }
-
-    case "Lazy": {
-      if (exp.cache) {
-        return formatExp(exp.cache)
-      } else {
-        return formatExp(exp.exp)
-      }
-    }
-
-    case "Fn": {
-      const { names, ret } = formatFn([exp.name], exp.ret)
-      return `(lambda (${names.join(" ")}) ${ret})`
-    }
-
-    case "Ap": {
-      const { target, args } = formatAp(exp.target, [formatExp(exp.arg)])
-      return `(${target} ${args.join(" ")})`
-    }
-
-    case "Let": {
-      const bindings = substitutionBindings(exp.substitution).map(formatBinding)
-      return `(let (${bindings.join(" ")}) ${formatExp(exp.body)})`
-    }
-  }
-}
-
-function formatFn(
-  names: Array<string>,
-  ret: Exp,
-): { names: Array<string>; ret: string } {
-  if (ret["@kind"] === "Fn") {
-    return formatFn([...names, ret.name], ret.ret)
-  } else {
-    return { names, ret: formatExp(ret) }
-  }
-}
-
-function formatAp(
-  target: Exp,
-  args: Array<string>,
-): { target: string; args: Array<string> } {
-  if (target["@kind"] === "Ap") {
-    return formatAp(target.target, [formatExp(target.arg), ...args])
-  } else {
-    return { target: formatExp(target), args }
-  }
-}
-
-function formatBinding(binding: Binding): string {
-  return `[${binding.name} ${formatExp(binding.exp)}]`
-}
diff --git a/src/lang1/format/index.ts b/src/lang1/format/index.ts
deleted file mode 100644
index 9567a6e..0000000
--- a/src/lang1/format/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./formatExp.js"
diff --git a/src/lang1/mod/Mod.ts b/src/lang1/mod/Mod.ts
deleted file mode 100644
index 13c8339..0000000
--- a/src/lang1/mod/Mod.ts
+++ /dev/null
@@ -1,10 +0,0 @@
-import { type Definition } from "../definition/index.js"
-import { type Stmt } from "../stmt/index.js"
-
-export type Mod = {
-  url: URL
-  loadedMods: Map<string, { mod: Mod; text: string }>
-  definitions: Map<string, Definition>
-  stmts: Array<Stmt>
-  isExecuted?: boolean
-}
diff --git a/src/lang1/mod/createMod.ts b/src/lang1/mod/createMod.ts
deleted file mode 100644
index b7ee3cf..0000000
--- a/src/lang1/mod/createMod.ts
+++ /dev/null
@@ -1,15 +0,0 @@
-import { type Mod } from "./Mod.js"
-
-export function createMod(options: {
-  url: URL
-  loadedMods: Map<string, { mod: Mod; text: string }>
-}): Mod {
-  const { url, loadedMods } = options
-
-  return {
-    url,
-    loadedMods,
-    definitions: new Map(),
-    stmts: [],
-  }
-}
diff --git a/src/lang1/mod/index.ts b/src/lang1/mod/index.ts
deleted file mode 100644
index 9edc1a7..0000000
--- a/src/lang1/mod/index.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-export * from "./Mod.js"
-export * from "./createMod.js"
-export * from "./modDefine.js"
-export * from "./modFind.js"
-export * from "./modResolve.js"
diff --git a/src/lang1/mod/modDefine.ts b/src/lang1/mod/modDefine.ts
deleted file mode 100644
index 41a2efa..0000000
--- a/src/lang1/mod/modDefine.ts
+++ /dev/null
@@ -1,18 +0,0 @@
-import type { Definition } from "../definition/Definition.js"
-import type { Mod } from "./Mod.js"
-import { modFind } from "./modFind.js"
-
-export function modDefine(
-  mod: Mod,
-  name: string,
-  definition: Definition,
-): void {
-  assertNotRedefine(mod, name)
-  mod.definitions.set(name, definition)
-}
-
-function assertNotRedefine(mod: Mod, name: string): void {
-  if (modFind(mod, name)) {
-    throw new Error(`I can not redefine name: ${name}`)
-  }
-}
diff --git a/src/lang1/mod/modFind.ts b/src/lang1/mod/modFind.ts
deleted file mode 100644
index 2c144a0..0000000
--- a/src/lang1/mod/modFind.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-import type { Definition } from "../definition/Definition.js"
-import type { Mod } from "./Mod.js"
-
-export function modFind(mod: Mod, name: string): Definition | undefined {
-  return mod.definitions.get(name)
-}
diff --git a/src/lang1/mod/modResolve.ts b/src/lang1/mod/modResolve.ts
deleted file mode 100644
index 5288b72..0000000
--- a/src/lang1/mod/modResolve.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-import { type Mod } from "./index.js"
-
-export function modResolve(mod: Mod, href: string): URL {
-  return new URL(href, mod.url)
-}
diff --git a/src/lang1/reduce/index.ts b/src/lang1/reduce/index.ts
deleted file mode 100644
index cc5d6f9..0000000
--- a/src/lang1/reduce/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./reduce.js"
diff --git a/src/lang1/reduce/lookup.ts b/src/lang1/reduce/lookup.ts
deleted file mode 100644
index fa03e71..0000000
--- a/src/lang1/reduce/lookup.ts
+++ /dev/null
@@ -1,15 +0,0 @@
-import { type Exp } from "../exp/index.js"
-import { type Substitution } from "../substitution/index.js"
-
-export function lookup(
-  name: string,
-  substitution: Substitution,
-): Exp | undefined {
-  for (const binding of substitution.values()) {
-    if (binding.name === name) {
-      return binding.exp
-    }
-  }
-
-  return undefined
-}
diff --git a/src/lang1/reduce/reduce.ts b/src/lang1/reduce/reduce.ts
deleted file mode 100644
index 0443a71..0000000
--- a/src/lang1/reduce/reduce.ts
+++ /dev/null
@@ -1,54 +0,0 @@
-import * as Exps from "../exp/index.js"
-import { type Exp } from "../exp/index.js"
-import { modFind, type Mod } from "../mod/index.js"
-import { substitutionInitial } from "../substitution/index.js"
-import { substitute } from "./substitute.js"
-
-// NOTE `reduce` might hit fixpoint on other kind of expressions,
-// but it will always remove `Let`.
-
-export function reduce(mod: Mod, exp: Exp): Exp {
-  switch (exp["@kind"]) {
-    case "Var": {
-      const defintion = modFind(mod, exp.name)
-      if (defintion) {
-        return reduce(mod, defintion.exp)
-      } else {
-        return exp
-      }
-    }
-
-    case "Lazy": {
-      if (exp.cache) {
-        return exp.cache
-      } else {
-        exp.cache = reduce(mod, exp.exp)
-        return exp.cache
-      }
-    }
-
-    case "Fn": {
-      return Exps.Fn(exp.name, reduce(mod, exp.ret))
-    }
-
-    case "Ap": {
-      const target = reduce(mod, exp.target)
-      const arg = Exps.Lazy(exp.arg)
-
-      switch (target["@kind"]) {
-        case "Fn": {
-          const substitution = substitutionInitial(target.name, arg)
-          return reduce(mod, substitute(substitution, target.ret))
-        }
-
-        default: {
-          return Exps.Ap(target, reduce(mod, arg))
-        }
-      }
-    }
-
-    case "Let": {
-      return reduce(mod, substitute(exp.substitution, exp.body))
-    }
-  }
-}
diff --git a/src/lang1/reduce/substitute.ts b/src/lang1/reduce/substitute.ts
deleted file mode 100644
index ef39a84..0000000
--- a/src/lang1/reduce/substitute.ts
+++ /dev/null
@@ -1,79 +0,0 @@
-import * as Exps from "../exp/index.js"
-import { type Exp } from "../exp/index.js"
-import {
-  substitutionExtend,
-  substitutionIsEmpty,
-  substitutionMapExp,
-  substitutionMerge,
-  substitutionTakeNames,
-  type Substitution,
-} from "../substitution/index.js"
-import { globalFreshen } from "../utils/globalFreshen.js"
-import { lookup } from "./lookup.js"
-
-// NOTE `substitute` should not call `reduce.
-
-export function substitute(substitution: Substitution, body: Exp): Exp {
-  substitution = substitutionTakeNames(
-    substitution,
-    Exps.expFreeNames(new Set(), body),
-  )
-
-  if (substitutionIsEmpty(substitution)) {
-    return body
-  }
-
-  switch (body["@kind"]) {
-    case "Var": {
-      const found = lookup(body.name, substitution)
-      if (found) {
-        return found
-      } else {
-        return body
-      }
-    }
-
-    case "Lazy": {
-      if (body.cache) {
-        return substitute(substitution, body.cache)
-      } else {
-        return Exps.Lazy(substitute(substitution, body.exp))
-      }
-    }
-
-    case "Fn": {
-      const freshName = globalFreshen(body.name)
-      return Exps.Fn(
-        freshName,
-        Exps.Let(
-          substitutionExtend(substitution, body.name, Exps.Var(freshName)),
-          body.ret,
-        ),
-      )
-    }
-
-    case "Ap": {
-      return Exps.Ap(
-        Exps.Let(substitution, body.target),
-        Exps.Let(substitution, body.arg),
-      )
-    }
-
-    case "Let": {
-      return substitute(
-        composeSubstitution(substitution, body.substitution),
-        body.body,
-      )
-    }
-  }
-}
-
-export function composeSubstitution(
-  left: Substitution,
-  right: Substitution,
-): Substitution {
-  return substitutionMerge(
-    left,
-    substitutionMapExp(right, (exp) => substitute(left, exp)),
-  )
-}
diff --git a/src/lang1/run/execute.ts b/src/lang1/run/execute.ts
deleted file mode 100644
index ab01d9f..0000000
--- a/src/lang1/run/execute.ts
+++ /dev/null
@@ -1,31 +0,0 @@
-import { formatExp } from "../format/formatExp.js"
-import { modDefine, type Mod } from "../mod/index.js"
-import { reduce } from "../reduce/reduce.js"
-import { type Stmt } from "../stmt/Stmt.js"
-import { importOne } from "./importOne.js"
-
-export function execute(mod: Mod, stmt: Stmt): null | string {
-  switch (stmt["@kind"]) {
-    case "Compute": {
-      const reducedExp = reduce(mod, stmt.exp)
-      return formatExp(reducedExp)
-    }
-
-    case "Define": {
-      modDefine(mod, stmt.name, {
-        mod,
-        name: stmt.name,
-        exp: stmt.exp,
-      })
-      return null
-    }
-
-    case "Import": {
-      for (const entry of stmt.entries) {
-        importOne(mod, stmt.path, entry)
-      }
-
-      return null
-    }
-  }
-}
diff --git a/src/lang1/run/executeMod.ts b/src/lang1/run/executeMod.ts
deleted file mode 100644
index 9cbd5a3..0000000
--- a/src/lang1/run/executeMod.ts
+++ /dev/null
@@ -1,18 +0,0 @@
-import type { Mod } from "../mod/index.js"
-import { execute } from "./execute.js"
-
-export function executeMod(mod: Mod): boolean {
-  if (mod.isExecuted) {
-    return false
-  }
-
-  for (const stmt of mod.stmts) {
-    const output = execute(mod, stmt)
-    if (output) {
-      console.log(output)
-    }
-  }
-
-  mod.isExecuted = true
-  return true
-}
diff --git a/src/lang1/run/importOne.ts b/src/lang1/run/importOne.ts
deleted file mode 100644
index c1f036c..0000000
--- a/src/lang1/run/importOne.ts
+++ /dev/null
@@ -1,29 +0,0 @@
-import { modDefine, modFind, modResolve } from "../mod/index.js"
-import type { Mod } from "../mod/Mod.js"
-import type { ImportEntry } from "../stmt/Stmt.js"
-import { executeMod } from "./executeMod.js"
-
-export function importOne(mod: Mod, path: string, entry: ImportEntry): void {
-  const url = modResolve(mod, path)
-  if (url.href === mod.url.href) {
-    throw new Error(`I can not circular import: ${path}`)
-  }
-
-  const found = mod.loadedMods.get(url.href)
-  if (found === undefined) {
-    throw new Error(`Mod is not loaded: ${path}`)
-  }
-
-  executeMod(found.mod)
-
-  const { name, rename } = entry
-
-  const def = modFind(found.mod, name)
-  if (def === undefined) {
-    throw new Error(
-      `I can not import undefined name: ${name}, from path: ${path}`,
-    )
-  }
-
-  modDefine(mod, rename || name, def)
-}
diff --git a/src/lang1/run/index.ts b/src/lang1/run/index.ts
deleted file mode 100644
index 89e8e9f..0000000
--- a/src/lang1/run/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./run.js"
diff --git a/src/lang1/run/load.ts b/src/lang1/run/load.ts
deleted file mode 100644
index d3229f3..0000000
--- a/src/lang1/run/load.ts
+++ /dev/null
@@ -1,48 +0,0 @@
-import { Fetcher } from "@cicada-lang/framework/lib/fetcher/index.js"
-import fs from "node:fs"
-import { ParsingError } from "../../sexp/index.js"
-import { createMod, modResolve, type Mod } from "../mod/index.js"
-import { type Stmt } from "../stmt/index.js"
-import { Parser } from "../syntax/index.js"
-
-const fetcher = new Fetcher()
-
-fetcher.register("file", (url) => fs.promises.readFile(url.pathname, "utf8"))
-
-export async function load(
-  url: URL,
-  loadedMods: Map<string, { mod: Mod; text: string }>,
-): Promise<Mod> {
-  const found = loadedMods.get(url.href)
-  if (found !== undefined) {
-    return found.mod
-  }
-
-  const text = await fetcher.fetch(url)
-
-  try {
-    const mod = createMod({ url, loadedMods })
-    mod.stmts = parseStmts(text)
-    loadedMods.set(url.href, { mod, text })
-
-    for (const stmt of mod.stmts) {
-      if (stmt["@kind"] === "Import") {
-        const importedUrl = modResolve(mod, stmt.path)
-        await load(importedUrl, loadedMods)
-      }
-    }
-
-    return mod
-  } catch (error) {
-    if (error instanceof ParsingError) {
-      throw new Error(error.report(text))
-    }
-
-    throw error
-  }
-}
-
-function parseStmts(text: string): Array<Stmt> {
-  const parser = new Parser()
-  return parser.parseStmts(text)
-}
diff --git a/src/lang1/run/run.ts b/src/lang1/run/run.ts
deleted file mode 100644
index 41ced45..0000000
--- a/src/lang1/run/run.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-import { executeMod } from "./executeMod.js"
-import { load } from "./load.js"
-
-export async function run(url: URL): Promise<void> {
-  const mod = await load(url, new Map())
-  executeMod(mod)
-}
diff --git a/src/lang1/stmt/Stmt.ts b/src/lang1/stmt/Stmt.ts
deleted file mode 100644
index 4c743c2..0000000
--- a/src/lang1/stmt/Stmt.ts
+++ /dev/null
@@ -1,54 +0,0 @@
-import { type Exp } from "../exp/index.js"
-
-export type Stmt = Compute | Define | Import
-
-export type Compute = {
-  "@type": "Stmt"
-  "@kind": "Compute"
-  exp: Exp
-}
-
-export function Compute(exp: Exp): Compute {
-  return {
-    "@type": "Stmt",
-    "@kind": "Compute",
-    exp,
-  }
-}
-
-export type Define = {
-  "@type": "Stmt"
-  "@kind": "Define"
-  name: string
-  exp: Exp
-}
-
-export function Define(name: string, exp: Exp): Define {
-  return {
-    "@type": "Stmt",
-    "@kind": "Define",
-    name,
-    exp,
-  }
-}
-
-export type ImportEntry = {
-  name: string
-  rename?: string
-}
-
-export type Import = {
-  "@type": "Stmt"
-  "@kind": "Import"
-  path: string
-  entries: Array<ImportEntry>
-}
-
-export function Import(path: string, entries: Array<ImportEntry>): Import {
-  return {
-    "@type": "Stmt",
-    "@kind": "Import",
-    path,
-    entries,
-  }
-}
diff --git a/src/lang1/stmt/index.ts b/src/lang1/stmt/index.ts
deleted file mode 100644
index b54cfa1..0000000
--- a/src/lang1/stmt/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./Stmt.js"
diff --git a/src/lang1/substitution/Substitution.ts b/src/lang1/substitution/Substitution.ts
deleted file mode 100644
index 20f20ea..0000000
--- a/src/lang1/substitution/Substitution.ts
+++ /dev/null
@@ -1,70 +0,0 @@
-import type { Exp } from "../exp/index.js"
-
-export type Binding = {
-  name: string
-  exp: Exp
-}
-
-export type Substitution = Map<string, Binding>
-
-export function substitutionIsEmpty(substitution: Substitution): boolean {
-  return substitution.size === 0
-}
-
-export function substitutionFromBindings(
-  bindings: Array<Binding>,
-): Substitution {
-  return new Map([
-    ...bindings.map<[string, Binding]>((binding) => [binding.name, binding]),
-  ])
-}
-
-export function substitutionBindings(
-  substitution: Substitution,
-): Array<Binding> {
-  return Array.from(substitution.values())
-}
-
-export function substitutionInitial(name: string, exp: Exp): Substitution {
-  return new Map([[name, { name, exp }]])
-}
-
-export function substitutionExtend(
-  substitution: Substitution,
-  name: string,
-  exp: Exp,
-): Substitution {
-  return new Map([...substitution, [name, { name, exp }]])
-}
-
-export function substitutionMerge(
-  left: Substitution,
-  right: Substitution,
-): Substitution {
-  return new Map([...left, ...right])
-}
-
-export function substitutionMapExp(
-  substitution: Substitution,
-  f: (exp: Exp) => Exp,
-): Substitution {
-  return new Map([
-    ...Array.from(substitution.values()).map<[string, Binding]>(
-      ({ name, exp }) => [name, { name, exp: f(exp) }],
-    ),
-  ])
-}
-
-export function substitutionTakeNames(
-  substitution: Substitution,
-  names: Set<string>,
-): Substitution {
-  const newSubstitution = new Map()
-  for (const [name, exp] of substitution) {
-    if (names.has(name)) {
-      newSubstitution.set(name, exp)
-    }
-  }
-
-  return newSubstitution
-}
diff --git a/src/lang1/substitution/index.ts b/src/lang1/substitution/index.ts
deleted file mode 100644
index 279cb45..0000000
--- a/src/lang1/substitution/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./Substitution.js"
diff --git a/src/lang1/syntax/Parser.ts b/src/lang1/syntax/Parser.ts
deleted file mode 100644
index 9721668..0000000
--- a/src/lang1/syntax/Parser.ts
+++ /dev/null
@@ -1,24 +0,0 @@
-import { Parser as SexpParser } from "../../sexp/index.js"
-import { type Stmt } from "../stmt/index.js"
-import { matchStmt } from "./matchStmt.js"
-
-export class Parser extends SexpParser {
-  constructor() {
-    super({
-      quotes: [
-        { mark: "'", symbol: "quote" },
-        { mark: ",", symbol: "unquote" },
-        { mark: "`", symbol: "quasiquote" },
-      ],
-      parentheses: [
-        { start: "(", end: ")" },
-        { start: "[", end: "]" },
-      ],
-      comments: [";"],
-    })
-  }
-
-  parseStmts(text: string): Array<Stmt> {
-    return this.parseSexps(text).map(matchStmt)
-  }
-}
diff --git a/src/lang1/syntax/index.ts b/src/lang1/syntax/index.ts
deleted file mode 100644
index 25fb920..0000000
--- a/src/lang1/syntax/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./Parser.js"
diff --git a/src/lang1/syntax/matchExp.ts b/src/lang1/syntax/matchExp.ts
deleted file mode 100644
index e37b3d2..0000000
--- a/src/lang1/syntax/matchExp.ts
+++ /dev/null
@@ -1,53 +0,0 @@
-import { cons, match, matchList, v, type Sexp } from "../../sexp/index.js"
-import * as Exps from "../exp/index.js"
-import { type Exp } from "../exp/index.js"
-import {
-  substitutionFromBindings,
-  type Binding,
-} from "../substitution/index.js"
-import { matchName } from "./matchName.js"
-
-export function matchExp(sexp: Sexp): Exp {
-  return match<Exp>(sexp, [
-    [
-      ["lambda", v("names"), v("exp")],
-      ({ names, exp }) =>
-        matchList(names, matchName).reduceRight(
-          (fn, name) => Exps.Fn(name, fn),
-          matchExp(exp),
-        ),
-    ],
-
-    [
-      ["let", v("bindings"), v("body")],
-      ({ bindings, body }) =>
-        Exps.Let(
-          substitutionFromBindings(matchList(bindings, matchBinding)),
-          matchExp(body),
-        ),
-    ],
-
-    [
-      cons(v("target"), v("args")),
-      ({ target, args }) =>
-        matchList(args, matchExp).reduce(
-          (result, arg) => Exps.Ap(result, arg),
-          matchExp(target),
-        ),
-    ],
-
-    [v("name"), ({ name }, { span }) => Exps.Var(matchName(name))],
-  ])
-}
-
-export function matchBinding(sexp: Sexp): Binding {
-  return match<Binding>(sexp, [
-    [
-      [v("name"), v("exp")],
-      ({ name, exp }) => ({
-        name: matchName(name),
-        exp: matchExp(exp),
-      }),
-    ],
-  ])
-}
diff --git a/src/lang1/syntax/matchName.ts b/src/lang1/syntax/matchName.ts
deleted file mode 100644
index 830e22c..0000000
--- a/src/lang1/syntax/matchName.ts
+++ /dev/null
@@ -1,15 +0,0 @@
-import { ParsingError, matchSymbol, type Sexp } from "../../sexp/index.js"
-import { numberSubscripts } from "../../utils/stringToSubscript.js"
-
-export function matchName(sexp: Sexp): string {
-  const nameString = matchSymbol(sexp)
-  const subscripts = Object.values(numberSubscripts)
-  if (subscripts.some((subscript) => nameString.includes(subscript))) {
-    throw new ParsingError(
-      `[matchExp] A name should not include subscripts: ${nameString}`,
-      sexp.span,
-    )
-  }
-
-  return nameString
-}
diff --git a/src/lang1/syntax/matchStmt.ts b/src/lang1/syntax/matchStmt.ts
deleted file mode 100644
index ab64a10..0000000
--- a/src/lang1/syntax/matchStmt.ts
+++ /dev/null
@@ -1,62 +0,0 @@
-import {
-  cons,
-  listToArray,
-  match,
-  matchList,
-  matchString,
-  matchSymbol,
-  v,
-  type Sexp,
-} from "../../sexp/index.js"
-import * as Exps from "../exp/index.js"
-import * as Stmts from "../stmt/index.js"
-import { type Stmt } from "../stmt/index.js"
-import { matchExp } from "./matchExp.js"
-import { matchName } from "./matchName.js"
-
-export function matchStmt(sexp: Sexp): Stmt {
-  return match<Stmt>(sexp, [
-    [
-      ["define", cons(v("name"), v("args")), v("exp")],
-      ({ name, args, exp }) =>
-        Stmts.Define(
-          matchName(name),
-          matchList(args, matchName).reduceRight(
-            (fn, name) => Exps.Fn(name, fn),
-            matchExp(exp),
-          ),
-        ),
-    ],
-
-    [
-      ["define", v("name"), v("exp")],
-      ({ name, exp }) => Stmts.Define(matchName(name), matchExp(exp)),
-    ],
-
-    [
-      cons("import", v("body")),
-      ({ body }) => {
-        const sexps = listToArray(body)
-        const url = sexps[sexps.length - 1]
-        const entries = sexps.slice(0, sexps.length - 1)
-        return Stmts.Import(matchString(url), entries.map(matchImportEntry))
-      },
-    ],
-
-    [v("exp"), ({ exp }) => Stmts.Compute(matchExp(exp))],
-  ])
-}
-
-function matchImportEntry(sexp: Sexp): Stmts.ImportEntry {
-  return match<Stmts.ImportEntry>(sexp, [
-    [
-      ["rename", v("name"), v("rename")],
-      ({ name, rename }) => ({
-        name: matchSymbol(name),
-        rename: matchSymbol(rename),
-      }),
-    ],
-
-    [v("name"), ({ name }) => ({ name: matchSymbol(name) })],
-  ])
-}
diff --git a/src/lang1/utils/globalFreshen.ts b/src/lang1/utils/globalFreshen.ts
deleted file mode 100644
index 7976427..0000000
--- a/src/lang1/utils/globalFreshen.ts
+++ /dev/null
@@ -1,26 +0,0 @@
-import {
-  numberSubscripts,
-  stringToSubscript,
-} from "../../utils/stringToSubscript.js"
-
-export let globalNameCounters: Map<string, number> = new Map()
-
-export function globalFreshen(name: string): string {
-  name = nameWithoutSubscript(name)
-  const globalNameCounter = globalNameCounters.get(name)
-  if (globalNameCounter === undefined) {
-    globalNameCounters.set(name, 1)
-    const subscript = stringToSubscript(String(1))
-    return `${name}${subscript}`
-  } else {
-    globalNameCounters.set(name, globalNameCounter + 1)
-    const subscript = stringToSubscript(String(globalNameCounter + 1))
-    return `${name}${subscript}`
-  }
-}
-
-function nameWithoutSubscript(name: string): string {
-  const subscripts = Array.from(Object.values(numberSubscripts))
-  const chars = name.split("")
-  return chars.filter((char) => !subscripts.includes(char)).join("")
-}