-- Blase/Blase/AutoStructs/Defs.lean

import Blase.AutoStructs.ForMathlib

import Blase.SingleWidth.Defs

open Fin.NatCast

def liftMaxSucc1 (n m : Nat) : Fin (n + 1) → Fin (max n m + 2) :=
  fun k => if _ : k = n then Fin.last (max n m) else k.castLE (by admit /- proof elided -/
  )

def liftMaxSucc2 (n m : Nat) : Fin (m + 1) → Fin (max n m + 2) :=
  fun k => if _ : k = m then Fin.last (max n m + 1) else k.castLE (by admit /- proof elided -/
  )

def liftLast2 n : Fin 2 → Fin (n + 2)
| 0 => n
| 1 => Fin.last (n + 1)

def liftExcept2 n : Fin n → Fin (n + 2) :=
  fun k => Fin.castLE (by admit /- proof elided -/
  ) k

def liftMax1 (n m : Nat) : Fin n → Fin (max n m) :=
  fun k => k.castLE (by admit /- proof elided -/
  )

def liftMax2 (n m : Nat) : Fin m → Fin (max n m) :=
  fun k => k.castLE (by admit /- proof elided -/
  )

@[simp] def Term.evalFinBV (t : Term) (vars : Fin (arity t) → BitVec w) : BitVec w :=
  match t with
  | .var n => vars (Fin.last n)
  | .zero    => BitVec.zero w
  | .one     => 1
  | .negOne  => -1
  | .ofNat n => BitVec.ofNat _ n
  | .and t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ &&& x₂
  | .or t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ ||| x₂
  | .xor t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ ^^^ x₂
  | .not t     => ~~~(t.evalFinBV vars)
  
  | .add t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ + x₂
  | .sub t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ - x₂
  | .neg t       => -(t.evalFinBV vars)
  | .shiftL a n => (a.evalFinBV vars) <<< n

def Term.language (t : Term) : Set (BitVecs (t.arity + 1)) :=
  { bvs : BitVecs (t.arity + 1) | t.evalFinBV (fun n => bvs.bvs.get n) = bvs.bvs.get t.arity }

inductive RelationOrdering
| lt | le | gt | ge
deriving Repr, Fintype

inductive Relation
| eq
| signed (ord : RelationOrdering)
| unsigned (ord : RelationOrdering)
deriving Repr

def evalRelation (rel : Relation) {w} (bv1 bv2 : BitVec w) : Prop :=
  match rel with
  | .eq => bv1 = bv2
  | .signed .lt => bv1.slt bv2
  | .signed .le => bv1.sle  bv2
  | .signed .gt => bv2.slt bv1
  | .signed .ge => bv2.sle bv1
  | .unsigned .lt => bv1.ult bv2
  | .unsigned .le => bv1.ule bv2
  | .unsigned .gt => bv2.ult bv1
  | .unsigned .ge => bv2.ule bv1

@[simp]
def Relation.language (rel : Relation) : Set (BitVecs 2) :=
  { bvs | evalRelation rel (bvs.bvs.get 0) (bvs.bvs.get 1) }

inductive Binop
| and | or | impl | equiv
deriving Repr

def evalBinop (op : Binop) (b1 b2 : Prop) : Prop :=
  match op with
  | .and => b1 ∧ b2
  | .or => b1 ∨ b2
  | .impl => b1 → b2
  | .equiv => b1 ↔ b2

def langBinop (op : Binop) (l1 l2 : Set (BitVecs n)) : Set (BitVecs n) :=
  match op with
  | .and => l1 ∩ l2
  | .or => l1 ∪ l2
  | .impl => l1ᶜ ∪ l2
  | .equiv => (l1ᶜ ∪ l2) ∩ (l2ᶜ ∪ l1)

inductive Unop
| neg
deriving Repr

inductive Formula : Type
| width : WidthPredicate → Nat → Formula
| atom : Relation → Term → Term → Formula
| msbSet : Term → Formula
| unop : Unop → Formula → Formula
| binop : Binop → Formula → Formula → Formula
deriving Repr

@[simp]
def Formula.arity : Formula → Nat
| width _ _ => 0
| atom _ t1 t2 => max t1.arity t2.arity
| msbSet t => t.arity
| unop _ φ => φ.arity
| binop _ φ1 φ2 => max φ1.arity φ2.arity

@[simp]
def WidthPredicate.sat (wp : WidthPredicate) (w n : Nat) : Bool :=
  match wp with
  | .eq => w = n
  | .neq => w ≠ n
  | .lt => w < n
  | .le => w ≤ n
  | .gt => w > n
  | .ge => w ≥ n

@[simp]
def Formula.sat {w : Nat} (φ : Formula) (ρ : Fin φ.arity → BitVec w) : Prop :=
  match φ with
  | .width wp n => wp.sat w n
  | .atom rel t1 t2 =>
    let bv1 := t1.evalFinBV (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    let bv2 := t2.evalFinBV (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    evalRelation rel bv1 bv2
  | .unop .neg φ => ¬ φ.sat ρ
  | .binop op φ1 φ2 =>
    let b1 := φ1.sat (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    let b2 := φ2.sat (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    evalBinop op b1 b2
  | .msbSet t => (t.evalFinBV ρ).msb

@[simp]
def _root_.Set.lift (f : Fin n → Fin m) (bvs : Set (BitVecs n)) : Set (BitVecs m) :=
  BitVecs.transport f ⁻¹' bvs

@[simp]
def _root_.Set.proj (f : Fin n → Fin m) (bvs : Set (BitVecs m)) : Set (BitVecs n) :=
  BitVecs.transport f '' bvs

@[simp]
def langMsb : Set (BitVecs 1) := { bvs | bvs.bvs.get 0 |>.msb }

@[simp]
def Formula.language (φ : Formula) : Set (BitVecs φ.arity) :=
  match φ with
  | .width wp n => { bvs | wp.sat bvs.w n }
  | .atom rel t1 t2 =>
    let l1 := t1.language.lift (liftMaxSucc1 (FinEnum.card $ Fin t1.arity) (FinEnum.card $ Fin t2.arity))
    let l2 := t2.language.lift (liftMaxSucc2 (FinEnum.card $ Fin t1.arity) (FinEnum.card $ Fin t2.arity))
    let lrel := rel.language.lift $ liftLast2 (max (FinEnum.card (Fin t1.arity)) (FinEnum.card (Fin t2.arity)))
    let l := lrel ∩ l1 ∩ l2
    l.proj (liftExcept2 _)
  | .unop .neg φ => φ.languageᶜ
  | .binop op φ1 φ2 =>
    let l1 := φ1.language.lift $ liftMax1 φ1.arity φ2.arity
    let l2 := φ2.language.lift $ liftMax2 φ1.arity φ2.arity
    langBinop op l1 l2
  | .msbSet t =>
    let lmsb := langMsb.lift $ fun _ => Fin.last t.arity
    let l' := t.language ∩ lmsb
    l'.proj fun n => n.castLE (by admit /- proof elided -/
    )

-- Repository definitions used:
content: syntax "max" : MLIR.Pretty.uniform_op

content: 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) )

content: 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))

content: 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) )

content: 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) )

content: inductive WidthPredicate
| eq
| neq
| lt
| le
| gt
| ge
deriving Repr, Inhabited, Lean.ToExpr

content: structure BitVecs (n : Nat) where
  w : Nat
  bvs : List.Vector (BitVec w) n

content: inductive Term : Type
| var : Nat → Term
 
| zero : Term
 
| negOne : Term
 
| one : Term
 
| ofNat (n : Nat) : Term
 
| and : Term → Term → Term
 
| or : Term → Term → Term
 
| xor : Term → Term → Term
 
| not : Term → Term
 
| add : Term → Term → Term
 
| sub : Term → Term → Term
 
| neg : Term → Term


 
| shiftL : Term → Nat → Term


deriving Repr, Inhabited, Lean.ToExpr

content: @[simp] def Term.arity : Term → Nat
| (var n) => n+1
| zero => 0
| one => 0
| negOne => 0
| ofNat _ => 0
| Term.and t₁ t₂ => max (arity t₁) (arity t₂)
| Term.or t₁ t₂ => max (arity t₁) (arity t₂)
| Term.xor t₁ t₂ => max (arity t₁) (arity t₂)
| Term.not t => arity t
| add t₁ t₂ => max (arity t₁) (arity t₂)
| sub t₁ t₂ => max (arity t₁) (arity t₂)
| neg t => arity t


| shiftL t .. => arity t

content: def BitVecs.transport (f : Fin n → Fin m) (bvs : BitVecs m) : BitVecs n :=
  { w := bvs.w, bvs := bvs.bvs.transport f }

content: def BitVec.transport (f : Fin n2 → Fin n1) (bv : BitVec n1) : BitVec n2 :=
  BitVec.ofFn fun i => bv.getLsbD (f i)

content: def BitVec.ofFn {w : Nat} (f : Fin w → Bool) : BitVec w :=
  BitVec.iunfoldr (fun i _ => ((), f i)) () |>.2

content: def List.Vector.transport (v : Vector α m) (f : Fin n → Fin m) : Vector α n :=
  Vector.ofFn fun i => v.get (f i)

content: def BitVecs'.transport (f : Fin n → Fin m) (bvs' : BitVecs' m): BitVecs' n :=
  bvs'.map fun bv => bv.transport f

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

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

content: infixr:67 "::ᵥ" => Valuation.cons

-- Repository lemmas used:
content: @[simp]
lemma List.Vector.append_get_ge {x : List.Vector α n} {y : List.Vector α m} {i : Fin (n+m)} (hlt: n ≤ i) :
    (x ++ y).get i = y.get ((i.cast (Nat.add_comm n m) |>.subNat n hlt))

content: @[simp]
lemma List.Vector.append_get_lt {x : List.Vector α n} {y : List.Vector α m} {i : Fin (n+m)} (hlt: i < n) :
    (x ++ y).get i = x.get (i.castLT hlt)

content: @[simp]
lemma BitVecs.transport_getElem {bvs : BitVecs m} (f : Fin n → Fin m) (i : Fin n) :
    (bvs.transport f).bvs.get i = bvs.bvs.get (f i)

-- Local definitions used:
content: def liftMaxSucc1 (n m : Nat) : Fin (n + 1) → Fin (max n m + 2) :=
  fun k => if _ : k = n then Fin.last (max n m) else k.castLE (by admit /- proof elided -/
  )

content: def liftMaxSucc2 (n m : Nat) : Fin (m + 1) → Fin (max n m + 2) :=
  fun k => if _ : k = m then Fin.last (max n m + 1) else k.castLE (by admit /- proof elided -/
  )

content: def liftLast2 n : Fin 2 → Fin (n + 2)
| 0 => n
| 1 => Fin.last (n + 1)

content: def liftExcept2 n : Fin n → Fin (n + 2) :=
  fun k => Fin.castLE (by admit /- proof elided -/
  ) k

content: def liftMax1 (n m : Nat) : Fin n → Fin (max n m) :=
  fun k => k.castLE (by admit /- proof elided -/
  )

content: def liftMax2 (n m : Nat) : Fin m → Fin (max n m) :=
  fun k => k.castLE (by admit /- proof elided -/
  )

content: @[simp] def Term.evalFinBV (t : Term) (vars : Fin (arity t) → BitVec w) : BitVec w :=
  match t with
  | .var n => vars (Fin.last n)
  | .zero    => BitVec.zero w
  | .one     => 1
  | .negOne  => -1
  | .ofNat n => BitVec.ofNat _ n
  | .and t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ &&& x₂
  | .or t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ ||| x₂
  | .xor t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ ^^^ x₂
  | .not t     => ~~~(t.evalFinBV vars)
  
  | .add t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ + x₂
  | .sub t₁ t₂ =>
      let x₁ := t₁.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      let x₂ := t₂.evalFinBV (fun i => vars (Fin.castLE (by admit /- proof elided -/
      ) i))
      x₁ - x₂
  | .neg t       => -(t.evalFinBV vars)
  | .shiftL a n => (a.evalFinBV vars) <<< n

content: def Term.language (t : Term) : Set (BitVecs (t.arity + 1)) :=
  { bvs : BitVecs (t.arity + 1) | t.evalFinBV (fun n => bvs.bvs.get n) = bvs.bvs.get t.arity }

content: inductive RelationOrdering
| lt | le | gt | ge
deriving Repr, Fintype

content: inductive Relation
| eq
| signed (ord : RelationOrdering)
| unsigned (ord : RelationOrdering)
deriving Repr

content: def evalRelation (rel : Relation) {w} (bv1 bv2 : BitVec w) : Prop :=
  match rel with
  | .eq => bv1 = bv2
  | .signed .lt => bv1.slt bv2
  | .signed .le => bv1.sle  bv2
  | .signed .gt => bv2.slt bv1
  | .signed .ge => bv2.sle bv1
  | .unsigned .lt => bv1.ult bv2
  | .unsigned .le => bv1.ule bv2
  | .unsigned .gt => bv2.ult bv1
  | .unsigned .ge => bv2.ule bv1

content: @[simp]
def Relation.language (rel : Relation) : Set (BitVecs 2) :=
  { bvs | evalRelation rel (bvs.bvs.get 0) (bvs.bvs.get 1) }

content: inductive Binop
| and | or | impl | equiv
deriving Repr

content: def evalBinop (op : Binop) (b1 b2 : Prop) : Prop :=
  match op with
  | .and => b1 ∧ b2
  | .or => b1 ∨ b2
  | .impl => b1 → b2
  | .equiv => b1 ↔ b2

content: def langBinop (op : Binop) (l1 l2 : Set (BitVecs n)) : Set (BitVecs n) :=
  match op with
  | .and => l1 ∩ l2
  | .or => l1 ∪ l2
  | .impl => l1ᶜ ∪ l2
  | .equiv => (l1ᶜ ∪ l2) ∩ (l2ᶜ ∪ l1)

content: inductive Unop
| neg
deriving Repr

content: inductive Formula : Type
| width : WidthPredicate → Nat → Formula
| atom : Relation → Term → Term → Formula
| msbSet : Term → Formula
| unop : Unop → Formula → Formula
| binop : Binop → Formula → Formula → Formula
deriving Repr

content: @[simp]
def Formula.arity : Formula → Nat
| width _ _ => 0
| atom _ t1 t2 => max t1.arity t2.arity
| msbSet t => t.arity
| unop _ φ => φ.arity
| binop _ φ1 φ2 => max φ1.arity φ2.arity

content: @[simp]
def WidthPredicate.sat (wp : WidthPredicate) (w n : Nat) : Bool :=
  match wp with
  | .eq => w = n
  | .neq => w ≠ n
  | .lt => w < n
  | .le => w ≤ n
  | .gt => w > n
  | .ge => w ≥ n

content: @[simp]
def Formula.sat {w : Nat} (φ : Formula) (ρ : Fin φ.arity → BitVec w) : Prop :=
  match φ with
  | .width wp n => wp.sat w n
  | .atom rel t1 t2 =>
    let bv1 := t1.evalFinBV (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    let bv2 := t2.evalFinBV (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    evalRelation rel bv1 bv2
  | .unop .neg φ => ¬ φ.sat ρ
  | .binop op φ1 φ2 =>
    let b1 := φ1.sat (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    let b2 := φ2.sat (fun n => ρ $ Fin.castLE (by admit /- proof elided -/
    ) n)
    evalBinop op b1 b2
  | .msbSet t => (t.evalFinBV ρ).msb

content: @[simp]
def _root_.Set.lift (f : Fin n → Fin m) (bvs : Set (BitVecs n)) : Set (BitVecs m) :=
  BitVecs.transport f ⁻¹' bvs

content: @[simp]
def _root_.Set.proj (f : Fin n → Fin m) (bvs : Set (BitVecs m)) : Set (BitVecs n) :=
  BitVecs.transport f '' bvs

content: @[simp]
def langMsb : Set (BitVecs 1) := { bvs | bvs.bvs.get 0 |>.msb }

content: @[simp]
def Formula.language (φ : Formula) : Set (BitVecs φ.arity) :=
  match φ with
  | .width wp n => { bvs | wp.sat bvs.w n }
  | .atom rel t1 t2 =>
    let l1 := t1.language.lift (liftMaxSucc1 (FinEnum.card $ Fin t1.arity) (FinEnum.card $ Fin t2.arity))
    let l2 := t2.language.lift (liftMaxSucc2 (FinEnum.card $ Fin t1.arity) (FinEnum.card $ Fin t2.arity))
    let lrel := rel.language.lift $ liftLast2 (max (FinEnum.card (Fin t1.arity)) (FinEnum.card (Fin t2.arity)))
    let l := lrel ∩ l1 ∩ l2
    l.proj (liftExcept2 _)
  | .unop .neg φ => φ.languageᶜ
  | .binop op φ1 φ2 =>
    let l1 := φ1.language.lift $ liftMax1 φ1.arity φ2.arity
    let l2 := φ2.language.lift $ liftMax2 φ1.arity φ2.arity
    langBinop op l1 l2
  | .msbSet t =>
    let lmsb := langMsb.lift $ fun _ => Fin.last t.arity
    let l' := t.language ∩ lmsb
    l'.proj fun n => n.castLE (by admit /- proof elided -/
    )

-- Local lemmas used:
content: lemma evalFin_eq {t : Term} {vars1 : Fin t.arity → BitVec w1} {vars2 : Fin t.arity → BitVec w2} :
    ∀ (heq : w1 = w2),
    (∀ n, vars1 n = heq ▸ vars2 n) →
    t.evalFinBV vars1 = heq ▸ t.evalFinBV vars2

content: @[simp]
lemma evalRelation_coe (rel : Relation) (bv1 bv2 : BitVec w1) (heq : w1 = w2) :
    evalRelation rel (heq ▸ bv1) (heq ▸ bv2) = evalRelation rel bv1 bv2

content: lemma helper1 : (k = 0) → (x ::ᵥ vs).get k = x

content: lemma helper2 : (k = 1) → (x ::ᵥ y ::ᵥ vs).get k = y

content: lemma formula_language_case_atom :
    let φ := Formula.atom rel t1 t2
    φ.language = λ (bvs : BitVecs φ.arity) => φ.sat (fun k => bvs.bvs.get k)

-- Target theorem and proof:
theorem formula_language (φ : Formula) :
    φ.language = { (bvs : BitVecs φ.arity) | φ.sat (fun k => bvs.bvs.get k) }
:= by
  let n : Nat := φ.arity
  induction φ
  case width wp n =>
    simp
  case atom rel t1 t2 =>
    apply formula_language_case_atom
  case unop op φ ih =>
    rcases op; simp [ih, Set.compl_def]
  case binop op φ1 φ2 ih1 ih2 =>
    unfold Formula.language
    ext1 bvs
    simp [ih1, ih2]
    have heq1 : (φ1.sat fun k => bvs.bvs.get (liftMax1 φ1.arity φ2.arity k)) ↔
           (φ1.sat fun n => bvs.bvs.get (Fin.castLE (by simp) n)) := by
      congr!
    have heq2 : (φ2.sat fun k => bvs.bvs.get (liftMax2 φ1.arity φ2.arity k)) = true ↔
           (φ2.sat fun n => bvs.bvs.get (Fin.castLE (by simp) n)) = true := by
      congr!
    rcases op <;>
      simp [evalBinop, langBinop, Set.instMembership] <;> simp_all <;> tauto
  case msbSet t =>
    ext1 bvs; simp only [Formula.arity, Formula.language, Set.proj, Set.lift, langMsb, Fin.isValue,
      Set.preimage_setOf_eq, Set.mem_image, Set.mem_inter_iff,
      Set.mem_setOf_eq, Formula.sat]
    rcases bvs with ⟨w, bvs⟩
    constructor
    · rintro ⟨bvsb, ⟨ht, hmsb⟩, heq⟩
      simp only [Fin.isValue, Formula.arity] at ht hmsb ⊢
      unfold Term.language at ht
      simp only [BitVecs.transport, List.Vector.transport] at hmsb
      simp at ht; rw [←ht] at hmsb; rw [←hmsb]
      simp [BitVecs.transport] at heq
      obtain ⟨hw, hbvs⟩ := heq
      simp; congr 1; simp [hw]
      rcases hw; simp
      congr 1; ext1 k
      simp at hbvs; simp [←hbvs, List.Vector.transport]; congr
    · intros heq
      use ⟨w,
        bvs ++ ((t.evalFinBV fun k => bvs.get $ k.castLE (by simp)) ::ᵥ List.Vector.nil)⟩
      unfold Term.language
      simp [BitVecs.transport, List.Vector.transport] at heq ⊢
      constructor; assumption
      ext1 k; simp; congr 1