From 96d71dd7def9d86e1bdb7cbc88a7368c90c9f73a Mon Sep 17 00:00:00 2001
From: eyihluyc <theviolthevioletandthewine@gmail.com>
Date: Fri, 15 Mar 2024 16:54:14 +0500
Subject: [PATCH] Add syntax and reduction

---
 Extended/.gitkeep      |   0
 Extended/Calculus.lean | 163 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 163 insertions(+)
 delete mode 100644 Extended/.gitkeep
 create mode 100644 Extended/Calculus.lean

diff --git a/Extended/.gitkeep b/Extended/.gitkeep
deleted file mode 100644
index e69de29b..00000000
diff --git a/Extended/Calculus.lean b/Extended/Calculus.lean
new file mode 100644
index 00000000..26df3c87
--- /dev/null
+++ b/Extended/Calculus.lean
@@ -0,0 +1,163 @@
+set_option autoImplicit false
+
+@[reducible]
+def Attr := String
+
+mutual
+  inductive OptionalAttr where
+    | attached : Term → OptionalAttr
+    | void : OptionalAttr
+
+  inductive Bindings : List Attr → Type where
+    | nil : Bindings []
+    | cons
+      : { lst : List Attr }
+      → (a : Attr)
+      → a ∉ lst
+      → OptionalAttr
+      → Bindings lst
+      → Bindings (a :: lst)
+
+  inductive Term : Type where
+    | obj : { lst : List Attr } → Bindings lst → Term
+    | dot : Term → Attr → Term
+    | app : Term → Attr → Term → Term
+    | ξ   : Term
+    | Φ   : Term
+end
+open OptionalAttr
+open Term
+
+
+-- def substitute (tξ : Term) (tΦ : Term) : Term → Term
+--   | obj o => obj o
+--   | dot t a => dot (substitute tξ tΦ t) a
+--   | app t a u => app (substitute tξ tΦ t) a (substitute tξ tΦ u)
+--   | ξ => tξ
+--   | Φ => tΦ
+
+def substitute (tξ : Term) : Term → Term
+  | obj o => obj o
+  | dot t a => dot (substitute tξ t) a
+  | app t a u => app (substitute tξ t) a (substitute tξ u)
+  | ξ => tξ
+  | Φ => Φ
+
+def lookup { lst : List Attr } (l : Bindings lst) (a : Attr)
+  : Option OptionalAttr
+  := match l with
+    | Bindings.nil => none
+    | Bindings.cons name _ opAttr tail =>
+        if (name == a) then some opAttr
+        else lookup tail a
+
+def insert
+  { lst : List Attr }
+  (l : Bindings lst)
+  (a : Attr)
+  (u : OptionalAttr)
+  : (Bindings lst)
+  := match l with
+    | Bindings.nil => Bindings.nil
+    | Bindings.cons name not_in opAttr tail =>
+        if name == a then Bindings.cons name not_in u tail
+        else Bindings.cons name not_in opAttr (insert tail a u)
+
+def has_no_void_attrs { lst : List Attr } : Bindings lst → Bool
+  | Bindings.nil => true
+  | Bindings.cons _ _ u tail => match u with
+    | void => false
+    | attached _ => has_no_void_attrs tail
+
+@[reducible]
+def Context := Term
+
+inductive Reduce : Context → Term → Term → Type where
+  | congOBJ
+    : { a : Attr }
+    → { t t' : Term }
+    → { attrs : List Attr }
+    → { bnds : Bindings attrs }
+    → { ctx : Context }
+    → has_no_void_attrs bnds
+    → lookup bnds a = some (attached t)
+    → Reduce ctx t t'
+    → Reduce ctx
+      (obj bnds)
+      (obj (insert bnds a (attached t')))
+  | congDOT
+    : { a : Attr }
+    → { t t' : Term }
+    → { ctx : Context }
+    → Reduce ctx t t'
+    → Reduce ctx (dot t a) (dot t' a)
+  | congAPPₗ
+    : { a : Attr }
+    → { t t' u : Term }
+    → { ctx : Context }
+    → Reduce ctx t t'
+    → Reduce ctx (app t a u) (app t' a u)
+  | congAPPᵣ
+    : { a : Attr }
+    → { t u u' : Term }
+    → { ctx : Context }
+    → Reduce ctx u u'
+    → Reduce ctx (app t a u) (app t a u')
+  | dot_c
+    : (ctx : Context)
+    → (t : Term)
+    → (c : Attr)
+    → { lst : List Attr }
+    → (l : Bindings lst)
+    → lookup l c = some (attached t)
+    → Reduce ctx
+      (dot (obj l) c)
+      (app (substitute (obj l) t) "ρ" ξ)
+  | dot_ρ
+    : (ctx : Context)
+    → (t : Term)
+    → { lst : List Attr }
+    → (l : Bindings lst)
+    → lookup l "ρ" = some (attached t)
+    → Reduce ctx
+      (dot (obj l) "ρ")
+      (substitute (obj l) t)
+  | dot_φ
+    : (ctx : Context)
+    → (c : Attr)
+    → (tφ : Term)
+    → { lst : List Attr }
+    → (l : Bindings lst)
+    → lookup l c = none
+    → lookup l "φ" = some (attached tφ)
+    → Reduce ctx
+      (dot (obj l) c)
+      (dot (app (substitute (obj l) tφ) "ρ" ξ) c)
+  | dot_Φ
+    : (a : Attr)
+    → (t_a : Term)
+    → { lst : List Attr }
+    → (l : Bindings lst)
+    → lookup l a = some (attached t_a)
+    → Reduce (obj l)
+      (dot Φ a)
+      (app (substitute (obj l) t_a) "ρ" Φ)
+  | app_c
+    : (ctx : Context)
+    → (u : Term)
+    → (c : Attr)
+    → { lst : List Attr }
+    → (l : Bindings lst)
+    → lookup l c = some void
+    → Reduce ctx
+      (app (obj l) c u)
+      (obj (insert l c (attached u)))
+  | app_ρ
+    : (ctx : Context)
+    → (u : Term)
+    → { lst : List Attr }
+    → (l : Bindings lst)
+    → lookup l "ρ" = some _
+    → Reduce ctx
+      (app (obj l) "ρ" u)
+      (obj (insert l "ρ" (attached u)))