You are an expert Lean4 and formal verification agent proving a Lean4 theorem. Your output **must** strictly adhere to the specified format.

### Input Information
You will receive the following components, relevant to the target theorem:
* <used_lib_defs>...</used_lib_defs>: Imported library definitions directly used by the theorem.
* <used_repo_defs>...</used_repo_defs>: Definitions from the local project (but outside the current file), directly or transitively used by the theorem.
* <lib_lemmas>...</lib_lemmas>: Imported library lemmas/theorems that may assist the proof.
* <repo_lemmas>...</repo_lemmas>: Lemmas/theorems defined in the local project outside this file.
* <local_ctx>...</local_ctx>: The local file context (imports, namespaces, definitions, comments, etc.) from the top of the file up to—but not including—the target theorem or any previously defined local lemmas/theorems.
* <target_theorem>...</target_theorem>: The target theorem statement, ending with `:=`.

**Notes**
1. Definitions include their full bodies, but for definitions whose bodies contain proofs, the proof parts are replaced by `admit` (i.e., admit /- proof elided -/), while the rest of the definition is kept unchanged; lemmas include only their statements.
2. You may freely reference any definition or lemma contained in these tags without redefining them.
3. The tags for used definitions and helpful lemmas (used_lib_defs, used_repo_defs, lib_lemmas, repo_lemmas) may be omitted if empty.

### Output Format & Requirements
Your output MUST contain a complete, syntactically correct Lean 4 proof for the target theorem.

**Strict Output Structure:**
<reasoning> 
...
</reasoning> 

<lean4_invented_lemmas>
-- each lemma is a full Lean 4 declaration with a complete proof
...
</lean4_invented_lemmas>

<lean4_proof>
-- Lean 4 proof body of the target theorem
...
</lean4_proof>

**Requirements:**
1. <reasoning> and <lean4_invented_lemmas> are OPTIONAL. Include them only if they aid proof construction.
2. <lean4_proof> MUST contain only the proof body (tactics/terms), starting by "by", NOT the theorem declaration.
3. <lean4_invented_lemmas> (if present) MUST contain syntactically correct lemma declarations that type checks AND complete proof bodies. Defining a lemma using `axiom` is NOT allowed.
4. <reasoning> contains high-level proof planning.
5. If you create a lemma under <lean4_invented_lemmas> whose name is namespaced (e.g., X.Y.Z), you MUST always refer to it using its fully qualified name. Do NOT rely on shortened names. For example, write rw [X.Y.Z], not rw [Z] for invented lemmas.
6. All Lean 4 code MUST be syntactically correct. No `sorry`, `admit`, or non-Lean text. Comments allowed using `--` or `/- ... -/`.
7. Follow the tags and structure EXACTLY. No extra text before, between, or after the sections.
8. Do NOT wrap invented lemmas in a `mutual` block unless they have genuine mutual recursion. Declare each lemma independently.

### Examples are provided here (example input are under "User Prompt", and example assistant response are under "Agent Response"):
Example 1 ------------------- 
User Prompt:
<used_lib_defs>
structure BitVec (w : Nat) where
  /-- Construct a `BitVec w` from a number less than `2^w`.
  O(1), because we use `Fin` as the internal representation of a bitvector. -/
  ofFin ::

  /-- Interpret a bitvector as a number less than `2^w`.
  O(1), because we use `Fin` as the internal representation of a bitvector. -/
  toFin : Fin (hPow 2 w)
</used_lib_defs>

<repo_lemmas>
theorem List.getElem_append_left{α : Type u_1} {l₁ l₂ : List α} {i : Nat} (hn : i < l₁.length) :\n(l₁ ++ l₂)[i] = l₁[i]
</repo_lemmas>

<local_ctx>
import Mathlib.Computability.NFA
import Mathlib.Data.FinEnum
import Mathlib.Data.Rel
import Mathlib.Data.Vector.Basic
import Blase.AutoStructs.ForLean

open Set
open Mathlib
open SetRel

-- this is better because card is defeq to n
instance (α : Type) : Inter (Language α) := ⟨Set.inter⟩
instance (α : Type) : Union (Language α) := ⟨Set.union⟩

/--
The set of `n`-tuples of bit vectors of an arbitrary width.
-/
structure BitVecs (n : Nat) where
  w : Nat
  bvs : List.Vector (BitVec w) n

def BitVecs.cast (bvs : BitVecs n) (h : n = n') : BitVecs n' :=
  { w := bvs.w, bvs := h ▸ bvs.bvs }

abbrev BitVecs.empty : BitVecs n := ⟨0, List.Vector.replicate n .nil⟩
abbrev BitVecs.singleton {w : Nat} (bv : BitVec w) : BitVecs 1 := ⟨w, bv ::ᵥ .nil⟩
abbrev BitVecs.pair {w : Nat} (bv1 bv2 : BitVec w) : BitVecs 2 := ⟨w, bv1 ::ᵥ bv2 ::ᵥ .nil⟩

/--
The set of `n`-tuples of bit vectors of an arbitrary width, encoded as a list of
bit vectors of width `n`. The width of the encoded bit vectors is the length of
the list.
-/
abbrev BitVecs' (n : Nat) := List (BitVec n)

@[simps]
def dec (bvs' : BitVecs' n) : BitVecs n where
  w := bvs'.length
  bvs := List.Vector.ofFn fun k => BitVec.ofFn fun i => bvs'[i].getLsbD k

@[simp]
</local_ctx>

<target_theorem>
lemma dec_snoc n (bvs' : BitVecs' n) (a : BitVec n) :
  dec (bvs' ++ [a]) =
    { w := bvs'.length + 1
      bvs := List.Vector.ofFn fun k =>
        BitVec.cons (a.getLsbD k) ((dec bvs').bvs.get k) } :=
</target_theorem>

Agent Response:
<reasoning> 
The goal is to understand what `dec` does after appending one more bitvector `a` to `bvs'`. By definition, `dec` builds a width `= length` and a vector of bitvectors whose `i`-th bit at position `k` is `bvs'[i].getLsbD k`. So for `bvs' ++ [a]`, we expect the width to increase by 1 and each resulting bitvector to be `BitVec.cons` of the new bit coming from `a`.

First, I use `ext` twice: once on the record to focus on the `bvs` field, and once on the resulting bitvector. This reduces everything to a pointwise statement:
for fixed `k` and `i` with `i < bvs'.length + 1`,
the bit `(bvs' ++ [a])[i].getLsbD k` should match the bit at index `i` of `BitVec.cons (a.getLsbD k) ((dec bvs').bvs.get k)`.

At this point I need a clean description of indexing into `BitVec.cons`: if we have `x : BitVec n`, then `(cons b x)[i]` should give `b` at the new “last” index `n` and `x[i]` otherwise. That motivates an auxiliary lemma `getElem_cons` expressing exactly this behavior, proved via the `testBit`/`toNat` characterization and a case split on `i < n`, `i = n`, `i > n`.

Using `getElem_cons`, the RHS becomes an `if` on whether `i = bvs'.length`. So I split into cases:
- If `i = bvs'.length`, then `(bvs' ++ [a])[i]` is the appended `a`, so both sides reduce to `a.getLsbD k`.
- If `i ≠ bvs'.length`, the bound `i < bvs'.length + 1` forces `i < bvs'.length`. Then `(bvs' ++ [a])[i] = bvs'[i]` by `List.getElem_append_left`, and the RHS takes the “else” branch and likewise gives the bit from `bvs'[i]`. In both subcases, `simp` (plus the definition of `dec`) finishes.

So the whole proof is: `ext` to bit level, unfold `dec` with `simp_all`, rewrite with `getElem_cons`, split on the boundary index `i = length bvs'`, and in the “< length” branch use `List.getElem_append_left` and bounds to line up both sides.
</reasoning> 

<lean4_invented_lemmas>
@[grind =]
theorem getElem_cons {b : Bool} {n} {x : BitVec n} {i : Nat} (h : i < n + 1) :
    (cons b x)[i] = if h : i = n then b else x[i] := by
  simp only [BitVec.getElem_eq_testBit_toNat, BitVec.toNat_cons, Nat.testBit_or]
  rw [Nat.testBit_shiftLeft]
  rcases Nat.lt_trichotomy i n with i_lt_n | i_eq_n | n_lt_i
  · have p1 : ¬(n ≤ i) := by omega
    have p2 : i ≠ n := by omega
    simp [p1, p2]
  · simp only [i_eq_n, ge_iff_le, Nat.le_refl, decide_true, Nat.sub_self, Nat.testBit_zero,
    Bool.true_and, BitVec.testBit_toNat, BitVec.getLsbD_of_ge, Bool.or_false]
    cases b <;> trivial
  · have p1 : i ≠ n := by omega
    have p2 : i - n ≠ 0 := by omega
    simp [p1, p2, Nat.testBit_bool_toNat]
</lean4_invented_lemmas>

<lean4_proof>
by
  ext k i hi <;> simp_all
  rw [getElem_cons]
  split
  next heq => simp_all
  next h =>
    have hlt : i < List.length bvs' := by simp at hi; omega
    rw [List.getElem_append_left hlt]
    simp
</lean4_proof>

### Your task:
<used_lib_defs>
DecidableEq in Init.Prelude
Lean.ToExpr in Lean.ToExpr
List in Init.Prelude
Repr in Init.Data.Repr
Nat in Init.Prelude
AList in Mathlib.Data.List.AList
Option in Init.Prelude
StateT in Init.Control.State
Unit in Init.Prelude
String in Init.Prelude
BEq in Init.Prelude
ite in Init.Prelude
Vector in Init.Data.Vector.Basic
Bool in Init.Prelude
Int in Init.Data.Int.Basic
bool in Init.Control.Basic
Computation in Mathlib.Data.Seq.Computation
AList.insert in Mathlib.Data.List.AList
Valuation.map in Mathlib.RingTheory.Valuation.Basic
Exists in Init.Core
Id in Init.Control.Id
List.map in Init.Prelude
Polynomial.X in Mathlib.Algebra.Polynomial.Basic
ZMod in Mathlib.Data.ZMod.Defs
Sigma in Init.Core
Sigma.mk in Init.Core
liftM in Init.Prelude
Iff in Init.Core
IsEmpty in Mathlib.Logic.IsEmpty
id in Init.Prelude
PUnit in Init.Prelude
Pure in Init.Prelude
HEq in Init.Prelude
</used_lib_defs>

<used_repo_defs>
syntax "neg" : MLIR.Pretty.uniform_op

macro_rules
  | `(mlir_op| $res:mlir_op_operand = const ($x)
      $[: $outer_type]? ) => do
      let outer_type ← outer_type.getDM `(mlir_type| _)
      `(mlir_op| $res:mlir_op_operand = "const"()
          {val = $x:num : $outer_type} : ($outer_type) -> ($outer_type) )

macro_rules
  | `(mlir_op| $res:mlir_op_operand = li ($x)
     $[: $outer_type]?  ) => do
      let outer_type ← outer_type.getDM `(mlir_type| _ )
      `(mlir_op| $res:mlir_op_operand = "li"()
          {imm = $x:num : $outer_type } : ($outer_type) -> ($outer_type))

macro_rules
| `(mlir_op| $res:mlir_op_operand = $op1:MLIR.Pretty.RV.opWithImmediate $reg1 , $x : $t)  => do
    let some opName := MLIR.EDSL.Pretty.extractOpName op1.raw
      | Macro.throwUnsupported
    `(mlir_op| $res:mlir_op_operand = $opName ($reg1) {imm = $x:num : $t} : ($t) -> ($t) )

macro_rules
| `(mlir_op| $res:mlir_op_operand = $op1:MLIR.Pretty.RV.opWithShamt $reg1 , $x  : $t )  => do
    let some opName := MLIR.EDSL.Pretty.extractOpName op1.raw
      | Macro.throwUnsupported
    `(mlir_op| $res:mlir_op_operand = $opName ($reg1) {shamt = $x:num : $t}  : ($t) -> ($t) )

abbrev Mapping (Γ Δ : Ctxt Ty) : Type :=
  @AList (Σ t, Var Γ t) (fun x => Var Δ x.1)

structure Ctxt (Ty : Type) : Type where
  ofList :: toList : List Ty
  
  deriving Repr, Lean.ToExpr, DecidableEq

def Var (Γ : Ctxt Ty) (t : Ty) : Type :=
  { i : Nat // Γ[i]? = some t }

inductive Lets (Γ_in : Ctxt d.Ty) (eff : EffectKind) :
    (Γ_out : Ctxt d.Ty) → Type where
  | nil : Lets Γ_in eff Γ_in
  | var (body : Lets Γ_in eff Γ_out) (e : Expr d Γ_out eff t) : Lets Γ_in eff e.outContext

protected instance Expr.decidableEq [DecidableEq d.Op] [DecidableEq d.Ty] :
    {Γ : Ctxt d.Ty} → {ty : List d.Ty} → DecidableEq (Expr d Γ eff ty)
  | Γ, _, .mk op₁ rfl eff_le₁ arg₁ regArgs₁, .mk op₂ eq eff_le₂ arg₂ regArgs₂ =>
    if ho : op₁ = op₂ then by
      subst ho
      letI := HVector.decidableEq arg₁ arg₂
      letI := HVector.decidableEqReg regArgs₁ regArgs₂
      exact decidable_of_iff (arg₁ = arg₂ ∧ regArgs₁ = regArgs₂) (by admit /- proof elided -/
      )
    else isFalse (by admit /- proof elided -/
    )

def Var (Γ : Context Ty) (ty : Ty) : Type := { v : VarName // Γ.hasType v ty }

def Valuation.nil : Ctxt.Valuation (∅ : Ctxt Ty) := fun _ v => v.emptyElim

inductive EffectKind
| pure 
| impure 
deriving Repr, DecidableEq, Lean.ToExpr

def Valuation.cons {Γ : Ctxt Ty} {t : Ty} (x : toType t) (V : Γ.Valuation) :
    (Γ.cons t).Valuation :=

protected instance HVector.decidableEqReg [DecidableEq d.Op] [DecidableEq d.Ty] :
    ∀ {l : RegionSignature d.Ty}, DecidableEq (HVector (fun t => Com d t.1 .impure t.2) l)
  | _, .nil, .nil => isTrue rfl
  | _, .cons x₁ v₁, .cons x₂ v₂ =>
    letI := HVector.decidableEqReg v₁ v₂
    letI := Com.decidableEq x₁ x₂
    decidable_of_iff (x₁ = x₂ ∧ v₁ = v₂) (by admit /- proof elided -/
    )

@[elab_as_elim]
def appendCases
    {motive : (Γ ++ Δ).Var t → Sort u}
    (left : (v : Var Γ t) → motive (appendInl v))
    (right : (v : Var Δ t) → motive (appendInr v)) :
    (v : (Γ ++ Δ).Var t) → motive v
  | ⟨idx, h⟩ =>
    if hv : idx < Γ.length then
      left ⟨idx, by admit /- proof elided -/
      ⟩
    else
      let v' : Var _ _ := ⟨idx - Γ.length, by admit /- proof elided -/
      ⟩
      have eq : v'.appendInr = ⟨idx, h⟩ := by admit /- proof elided -/

@[match_pattern]
def last (Γ : Ctxt Ty) (t : Ty) : Ctxt.Var (Ctxt.cons t Γ) t :=
  ⟨0, by admit /- proof elided -/
  ⟩

def appendInl (v : Γ.Var t) : (Γ ++ Δ).Var t :=
  ⟨v.val, by admit /- proof elided -/
  ⟩

class TyDenote (β : Type) : Type 1 where
  toType : β → Type

def map (f : ∀ (a : α), A a → B a) :
    ∀ {l : List α}, HVector A l → HVector B l
  | [],   .nil        => .nil
  | t::_, .cons a as  => .cons (f t a) (map f as)

def map (f : Ty₁ → Ty₂) : Ctxt Ty₁ → Ctxt Ty₂ :=
  ofList ∘ (List.map f) ∘ toList

@[match_pattern]
def cons (hd : Ty) : Ctxt Ty → Ctxt Ty
| ⟨tl⟩ => ⟨hd :: tl⟩

noncomputable def f : (ZMod q)[X] := X^(2^n) + 1

def sig          := Signature.sig ∘ s.signature

structure Signature (Ty : Type) where
  mkEffectful ::
  sig         : List Ty
  regSig      : RegionSignature Ty
  returnTypes : List Ty
  effectKind  : EffectKind := .pure

class DialectSignature (d : Dialect) where
  signature : d.Op → Signature d.Ty

def effectKind   := Signature.effectKind ∘ s.signature

def returnTypes  := Signature.returnTypes ∘ s.signature

def Expr.ty : Expr d Γ eff [t] → d.Ty := fun _ => t

def Expr.op {Γ : Ctxt d.Ty} {eff : EffectKind} {ty} (e : Expr d Γ eff ty) : d.Op :=
  Expr.casesOn e (fun op _ _ _ _ => op)

class DialectDenote (d : Dialect) [TyDenote d.Ty] [DialectSignature d] where
  denote : (op : d.Op) → HVector toType (DialectSignature.sig op) →
    (HVector (fun t : Ctxt d.Ty × List d.Ty =>
      t.1.Valuation
      → EffectKind.impure.toMonad d.m (HVector toType t.2))
            (DialectSignature.regSig op)) →
    ((DialectSignature.effectKind op).toMonad d.m
      (HVector toType <| DialectSignature.returnTypes op))

def Lets.denote [DialectSignature d] [DialectDenote d] {Γ₂}
    (lets : Lets d Γ₁ eff Γ₂) (V : Valuation Γ₁) : (eff.toMonad d.m <| Valuation Γ₂) :=
  match lets with
  | .nil          => return V
  | .var lets' e  => lets'.denote V >>= e.denote

def regSig       := Signature.regSig ∘ s.signature

abbrev RegionSignature Ty := List (Ctxt Ty × List Ty)

inductive Ty (q : Nat) (n : Nat)
  | index : Ty q n
  | integer : Ty q n
  | tensor : Ty q n
  | polynomialLike : Ty q n
  deriving DecidableEq, Repr

structure Dialect where
  (Op : Type)
  (Ty : Type)
  (m : Type → Type := Id)

inductive Op (q : Nat) (n : Nat)
  | add : Op q n
  | sub : Op q n
  | mul : Op q n
  | mul_constant : Op q n
    
    
  | leading_term : Op q n
  | monomial : Op q n
  | monomial_mul : Op q n
  | from_tensor : Op q n
  | to_tensor : Op q n
  | const (c : R q n) : Op q n
  | const_int (c : Int) : Op q n
  | const_idx (i : Nat) : Op q n

@[simp]
instance Valuation.instAppendHVector (Γ : Ctxt Ty) (ts : List Ty) :
    HAppend (HVector toType ts) (Valuation Γ) (Valuation <| ⟨ts⟩ ++ Γ) where
  hAppend vals V :=
    (Valuation.ofHVector vals) ++ V

def HVector.denote :
    {l : RegionSignature d.Ty} → (T : HVector (fun t => Com d t.1 .impure t.2) l) →
    HVector (fun t => t.1.Valuation → EffectKind.impure.toMonad d.m (HVector toType t.2)) l
  | _, .nil => HVector.nil
  | _, .cons v vs => HVector.cons (v.denote) (HVector.denote vs)

@[simp] abbrev FlatCom.denote [DialectDenote d]
    (flatCom : FlatCom d Γ eff Γ_out ts)
    (V : Γ.Valuation) : eff.toMonad d.m (HVector toType ts) :=
  flatCom.lets.denote V >>= (return flatCom.rets.map ·)

structure FlatCom (d : Dialect) [DialectSignature d]  (Γ_in : Ctxt d.Ty) (eff : EffectKind)
    (Γ_out : Ctxt d.Ty) (ts : List d.Ty) where
  lets : Lets d Γ_in eff Γ_out
  rets : HVector Γ_out.Var ts

def RegionSignature.map (f : Ty → Ty') : RegionSignature Ty → RegionSignature Ty' :=
  List.map fun ⟨Γ, ty⟩ => (Γ.map f, ty.map f)

def Signature.map (f : Ty → Ty') : Signature Ty → Signature Ty' :=
  fun sig => {
    sig         := sig.sig.map f
    regSig      := sig.regSig.map f
    returnTypes := sig.returnTypes.map f
  }

inductive Com : Ctxt d.Ty → EffectKind → List d.Ty → Type where
  | rets {Γ} {tys} {eff : EffectKind} (vs : HVector Γ.Var tys) : Com Γ eff tys
  | var (e : Expr Γ eff ty) (body : Com (ty ++ Γ) eff β) : Com Γ eff β

def Expr.denote {ty} (e : Expr d Γ eff ty) (V : Valuation Γ) :
    eff.toMonad d.m (e.outContext.Valuation) :=
  match e with
  | ⟨op, ty_eq, heff, args, regArgs⟩ => do
      let argsDenote := args.map V
      let val ← EffectKind.liftEffect heff <| DialectDenote.denote op argsDenote regArgs.denote
      return (val ++ V).cast (by admit /- proof elided -/
      )

def Com.outContext {Γ} : Com d Γ eff ts → Ctxt d.Ty :=
  Com.rec' (motive := fun _ => Ctxt d.Ty)
    (@fun Γ _ => Γ) 
    (fun _ _ r => r) 

def Com.rec' {Γ} (com : Com d Γ eff t) : motive com :=
   
  Com.rec
    (motive_1 := fun _ _ _ _ => PUnit)
    (motive_2 := fun _ eff' t' c =>
      (h₁ : eff = eff') → (h₂ : t = t') → motive (h₁ ▸ h₂ ▸ c))
    (motive_3 := fun _ _ => PUnit)
    (fun _ _ _ _ _ _ => ⟨⟩) 
    (fun v h₁ h₂ => 
      cast (by admit /- proof elided -/
      ) <| rets (h₂ ▸ v))
    (fun e' body' _ r' h₁ h₂ => 
      let e := h₁ ▸ e'
      let body : Com _ _ eff t := cast (by admit /- proof elided -/
      ) body'
      let r : motive body := cast (by admit /- proof elided -/
      ) (r' h₁ h₂)
      cast (by admit /- proof elided -/
      ) <| var e body r)
    ⟨⟩
    (fun _ _ _ _ => ⟨⟩)
    com
    rfl
    rfl

def Valuation.cast {Γ Δ : Ctxt Ty} (h : Γ = Δ) (V : Valuation Γ) : Valuation Δ :=
  fun _ v => V <| v.castCtxt h.symm

abbrev Expr.outContext (_ : Expr d Γ eff ts) : Ctxt d.Ty :=
  ts ++ Γ

def liftEffect [Pure m] {e1 e2 : EffectKind} {α : Type}
    (hle : e1 ≤ e2) (v1 : e1.toMonad m α) : e2.toMonad m α :=
  match e1, e2, hle with
    | .pure, .pure, _ | .impure, .impure, _ => v1
    | .pure, .impure, _ => Pure.pure v1

def toMonad (e : EffectKind) (m : Type → Type) : Type → Type :=
  match e with
  | pure => Id
  | impure => m

def Com.denote : Com d Γ eff ty → (Γv : Valuation Γ) →
    eff.toMonad d.m (HVector toType ty)
  | .rets vs, Γv     => pure (vs.map Γv)
  | .var e body, V => e.denote V >>= body.denote

def Com.ty : Com d Γ eff [t] → d.Ty := fun _ => t

def Expr.args {Γ ts} (e : Expr d Γ eff ts) :
    HVector (Var Γ) (DialectSignature.sig e.op) :=
  Expr.casesOn e (fun _ _ _ args _ => args)

def Expr.regArgs {Γ ts} (e : Expr d Γ eff ts) :
    Regions d (DialectSignature.regSig e.op) :=
  Expr.casesOn e (fun _ _ _ _ regArgs => regArgs)

abbrev Regions (regSig : RegionSignature d.Ty) : Type :=
  HVector (fun t => Com d t.1 .impure t.2) regSig

def Expr.denoteOp (e : Expr d Γ eff ty) (V : Γ.Valuation) :
    eff.toMonad d.m (HVector toType ty) :=
  EffectKind.liftEffect e.eff_le <| cast (by admit /- proof elided -/
  ) <|
    DialectDenote.denote e.op (e.args.map V) e.regArgs.denote

infixr:50 "::ₕ" => HVector.cons

notation "⟦" x "⟧" => TyDenote.toType x

infixr:67 "::ᵥ" => Valuation.cons
</used_repo_defs>

<lib_lemmas>
Bool.false_eq_true in Init.Data.Bool
IsEmpty.exists_iff in Mathlib.Logic.IsEmpty
Option.isSome_none in Init.Data.Option.Basic
iff_false in Init.SimpLemmas
Option.get_some in Init.Data.Option.Basic
Option.isSome_iff_exists in Init.Data.Option.Lemmas
forall_exists_index in Init.PropLemmas
Exists.choose_spec in Init.Classical
</lib_lemmas>

<repo_lemmas>
@[simp] theorem map_cons : (Γ.cons a).map f = (Γ.map f).cons (f a)

theorem eq.ty_eq {v : Γ.Var t} {w : Γ.Var u} (h : v.eq w) : t = u

@[simp]
theorem Expr.op_mk {Γ : Ctxt d.Ty} {ty} {eff : EffectKind} (op : d.Op)
    (ty_eq : ty = DialectSignature.returnTypes op)
    (eff_le : DialectSignature.effectKind op ≤ eff)
    (args : HVector (Var Γ) (DialectSignature.sig op))
    (regArgs) :
    (Expr.mk op ty_eq eff_le args regArgs).op = op

@[simp]
theorem Expr.regArgs_mk {Γ : Ctxt d.Ty} {ty eff op}
    (ty_eq : ty = DialectSignature.returnTypes op)
    (eff_le : DialectSignature.effectKind op ≤ eff)
    (args : HVector (Var Γ) (DialectSignature.sig op)) (regArgs) :
    (Expr.mk op ty_eq eff_le args regArgs).regArgs = regArgs

@[simp] theorem appendCases_appendInl (v : Γ.Var t) :
    appendCases (motive := motive) left right v.appendInl = (left v)

@[simp]
theorem Expr.args_mk {Γ : Ctxt d.Ty} {ty eff op}
    (ty_eq : ty = DialectSignature.returnTypes op)
    (eff_le : DialectSignature.effectKind op ≤ eff)
    (args : HVector (Var Γ) (DialectSignature.sig op)) (regArgs) :
    (Expr.mk op ty_eq eff_le args regArgs).args = args

theorem Id.bind_eq' (x : Id α) (f : α → id β) : x >>= f = f x

@[simp] theorem Expr.denoteOp_eq_denoteOp_of {e₁ : Expr d Γ eff ty} {e₂ : Expr d Δ eff ty}
    {Γv : Valuation Γ} {Δv : Valuation Δ}
    (op_eq : e₁.op = e₂.op)
    (h_args : HVector.map Γv (op_eq ▸ e₁.args)
              = HVector.map Δv e₂.args)
    (h_regArgs : HEq e₁.regArgs.denote e₂.regArgs.denote) :
    e₁.denoteOp Γv = e₂.denoteOp Δv

theorem Id.pure_eq' (a : α) : (pure a : Id α) = a
</repo_lemmas>

<local_ctx>
import LeanMLIR.Framework

import LeanMLIR.Transforms.Rewrite.Mapping

open Ctxt (Var VarSet Valuation Hom)

variable {d} [DialectSignature d] [DecidableEq d.Ty]

variable {Γ : Ctxt d.Ty} {ty : d.Ty}

abbrev MatchVarM (Δ Γ : Ctxt d.Ty) := (StateT (Mapping Δ Γ) Option)

abbrev MatchVar (Δ Γ : Ctxt d.Ty)  := MatchVarM Δ Γ Unit

def MatchVarM.unifyVars {Δ Γ : Ctxt d.Ty} (v : Δ.Var t) (w : Γ.Var t) : MatchVar Δ Γ :=
  fun ma =>
    match ma.lookup ⟨_, v⟩ with
    | some v =>
      if v = w then
        some ((), ma)
      else
        none
    | none =>
      some ((), AList.insert ⟨_, v⟩ w ma)

open MatchVarM

variable [DecidableEq d.Op]

def matchArg [DecidableEq d.Op]
    (lets : Lets d Γ_in eff Γ_out) (matchLets : Lets d Δ_in .pure Δ_out) :
    {l : List d.Ty} → HVector (Var Γ_out) l → HVector (Var Δ_out) l →
    MatchVar Δ_in Γ_out
  | _, .nil, .nil => return
  | t::l, .cons vₗ vsₗ, .cons vᵣ vsᵣ => do
      matchVar (t := t) lets vₗ matchLets vᵣ
      matchArg lets matchLets vsₗ vsᵣ
  termination_by l => (sizeOf matchLets, l.length + 1)

def matchVar {Γ_in Γ_out Δ_in Δ_out : Ctxt d.Ty} {t : d.Ty} [DecidableEq d.Op]
    (lets : Lets d Γ_in eff Γ_out) (v : Var Γ_out t) :
    (matchLets : Lets d Δ_in .pure Δ_out) →
    (w : Var Δ_out t) →
    MatchVar Δ_in Γ_out
   
  | @Lets.var _ _ _ _ Δ_out ts matchLets matchExpr, w => by admit /- proof elided -/
      | right w =>
        exact matchVar lets v matchLets w
      | left w => exact do
        let ⟨ts', w', ie⟩ ← lets.getPureExpr v
        if hs : ∃ h : ie.op = matchExpr.op, ie.regArgs = (h ▸ matchExpr.regArgs) then
          have hts : Ctxt.ofList ts' = ts := by admit /- proof elided -/

end

section MatchVar

variable [DecidableEq d.Op] {Γ_in Γ_out Δ_in Δ_out t te}
          {lets : Lets d Γ_in eff Γ_out} {v : Var Γ_out t}
          {matchLets : Lets d Δ_in .pure Δ_out}
          {matchExpr : Expr d Δ_out .pure te}

variable (lets v matchLets w) (mapIn : Mapping _ _) in

def MatchVarResult := { mapOut : Mapping _ _ //
  ∃ (mapIn' mapOut' : Mapping _ _),
    mapIn.entries ⊆ mapIn'.entries
    ∧ mapOut'.entries ⊆ mapOut.entries
    ∧ matchVar lets v matchLets w mapIn' = some ((), mapOut') }

variable (lets matchLets) {tys} (vs ws : HVector _ tys) (mapIn : Mapping _ _) in

def MatchArgResult := { mapOut : Mapping _ _ //
  ∃ (mapIn' mapOut' : Mapping _ _),
    mapIn.entries ⊆ mapIn'.entries
    ∧ mapOut'.entries ⊆ mapOut.entries
    ∧ matchArg lets matchLets vs ws mapIn' = some ((), mapOut') }

namespace MatchVarResult

variable [TyDenote d.Ty] [∀ (t : d.Ty), Inhabited ⟦t⟧] in

section Left

variable {w : Δ_out.Var t}

def eqvVarLeft  :
    MatchVarResult lets v (.var matchLets matchExpr) w.appendInr ma
    ≃ MatchVarResult lets v matchLets w ma where
  toFun := fun ⟨x, h⟩ => ⟨x, by admit /- proof elided -/
  ⟩
  invFun := fun ⟨x, h⟩ => ⟨x, by admit /- proof elided -/
  ⟩

variable {mapIn} (mapOut : MatchVarResult lets v (.var matchLets matchExpr) w.appendInr mapIn)

end Left

variable {w : Var ⟨te⟩ _} {mapIn}

noncomputable def toArgResult
    (mapOut : MatchVarResult lets v (.var matchLets matchExpr) w.appendInl mapIn) :
    let args := mapOut.getPureExpr_eq_some.choose
    MatchArgResult lets matchLets args matchExpr.args mapIn :=
  ⟨mapOut.1, by admit /- proof elided -/
  ⟩

end MatchVarResult

end MatchVar

section SubsetEntries

open MatchVar

section UnifyVars

variable {Δ Γ : Ctxt d.Ty} {t} (w : Δ.Var t) (v : Γ.Var t)

end UnifyVars

variable [DecidableEq d.Op]

end SubsetEntries

namespace MatchArgResult

variable [DecidableEq d.Op] {Γ_in Γ_out Δ_in Δ_out te}
          {lets : Lets d Γ_in eff Γ_out}
          {matchLets : Lets d Δ_in .pure Δ_out}
          {matchExpr : Expr d Δ_out .pure te}
          {u us}
          {v : Γ_out.Var u} {vs : HVector Γ_out.Var us}
          {w : Δ_out.Var u} {ws : HVector Δ_out.Var us}
          {mapIn : Mapping _ _}
          (mapOut : MatchArgResult lets matchLets (v ::ₕ vs) (w ::ₕ ws) mapIn)

end MatchArgResult

section DenoteLemmas

variable [TyDenote d.Ty] [DecidableEq d.Op]

variable [∀ (t : d.Ty), Inhabited ⟦t⟧]

variable [Monad d.m] [LawfulMonad d.m] [DialectDenote d]

section DenoteIntoSubtype

end DenoteIntoSubtype

variable {Γ_in Γ_out Δ_in Δ_out : Ctxt d.Ty}
    {lets : Lets d Γ_in eff Γ_out}
    {matchLets : Lets d Δ_in .pure Δ_out}
</local_ctx>

<target_theorem>
theorem denote_matchVar
    {v w : Var _ t}
    (mapOut : MatchVarResult lets v matchLets w mapIn)
    (V : lets.ValidDenotation) :
    (matchLets.denote (mapOut.val.mapValuation V.val) w)
    = V.val v :=
</target_theorem>

