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:
* <all_available_defs>: Definitions available from imported modules (either from the current Lean repository or from Mathlib)
* <all_available_lemmas>: Lemmas/theorems available that may assist the proof.
* <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 available definitions and lemmas (all_available_defs, all_available_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:
<all_available_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)
</all_available_defs>

<all_available_lemmas>
theorem List.getElem_append_left{α : Type u_1} {l₁ l₂ : List α} {i : Nat} (hn : i < l₁.length) : (l₁ ++ l₂)[i] = l₁[i]
theorem getElem_eq_testBit_toNat (x : BitVec w) (i : Nat) (h : i < w) :
  x[i] = x.toNat.testBit i := rfl
@[simp, grind =] theorem toNat_cons (b : Bool) (x : BitVec w) :
    (cons b x).toNat = (b.toNat <<< w) ||| x.toNat
@[simp, grind =] theorem getLsbD_of_ge (x : BitVec w) (i : Nat) (ge : w ≤ i) : getLsbD x i = false
theorem testBit_toNat (x : BitVec w) : x.toNat.testBit i = x.getLsbD i
</all_available_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:
<all_available_defs>
Eq in Init.Prelude
id in Init.Prelude
BitVec in Init.Prelude
Nat in Init.Prelude
BitVec.cast in Init.Data.BitVec.Basic
BitVec.append in Init.Data.BitVec.Basic
BitVec.zero in Init.Data.BitVec.Basic
BitVec.extractLsb in Init.Data.BitVec.Basic

notation : 10 "GF(" term : 10 ")" => GaloisField term 1

class DCast (α : Sort*) (β : α → Sort*) where
  dcast : ∀ {a a' : α}, a = a' → β a → β a'
  dcast_id : ∀ {a : α}, dcast (Eq.refl a) = id

def AlgebraTowerEquiv.symm (e : AlgebraTowerEquiv A B) : AlgebraTowerEquiv B A where
  toRingEquiv := fun i => (e.toRingEquiv i).symm
  commutesLeft' := fun i j h r => by admit /- proof elided -/

structure AlgebraTowerEquiv (A : ι → Type*) [∀ i, CommSemiring (A i)] [a : AlgebraTower A]
  (B : ι → Type*) [∀ i, CommSemiring (B i)] [b : AlgebraTower B]
  where
    toRingEquiv : ∀ i, (A i ≃+* B i)
    commutesLeft' : ∀ (i j : ι) (h : i ≤ j) (r : A i),
      (b.algebraMap (i:=i) (j:=j) (h:=h)) ((toRingEquiv i) r) =
      (toRingEquiv j) (a.algebraMap (i:=i) (j:=j) (h:=h) r)

Function.LeftInverse in Init.Data.Function

@[ext]
structure OracleReduction {ι : Type} (oSpec : OracleSpec ι)
    (StmtIn : Type) {ιₛᵢ : Type} (OStmtIn : ιₛᵢ → Type) (WitIn : Type)
    (StmtOut : Type) {ιₛₒ : Type} (OStmtOut : ιₛₒ → Type) (WitOut : Type)
    {n : ℕ} (pSpec : ProtocolSpec n)
    [Oₛᵢ : ∀ i, OracleInterface (OStmtIn i)] [Oₘ : ∀ i, OracleInterface (pSpec.Message i)]
    where
  prover : OracleProver oSpec StmtIn OStmtIn WitIn StmtOut OStmtOut WitOut pSpec
  verifier : OracleVerifier oSpec StmtIn OStmtIn StmtOut OStmtOut pSpec

IsUnit in Mathlib.Algebra.Group.Units.Defs

MvPolynomial.isEmptyAlgEquiv in Mathlib.Algebra.MvPolynomial.Equiv

φ : ∀ i : Fin (M + 1), ∀ j : Fin ((P.foldingParam i) + 1), (indexPowT (S i) (P.φ i) j) ↪ F

instance instDCast₂ : DCast₂ Nat ProtocolSpec
    (fun _ pSpec => Prover oSpec StmtIn WitIn StmtOut WitOut pSpec) where
  dcast₂ := Prover.cast
  dcast₂_id := Prover.cast_id

inductive LeafData (α : Type) : Skeleton → Type
  | leaf (value : α) : LeafData α Skeleton.leaf
  | internal {left right} (leftData : LeafData α left) (rightData : LeafData α right) :
      LeafData α (Skeleton.internal left right)
  deriving Repr

instance : _root_.Field Field := ZMod.instField fieldSize

Vector.tail in Init.Data.Vector.Basic

instance [Zero T] [ToNat T] : DecidableRel (@LT.lt (Cayley T) _) := fun a b =>
  Nat.decLt (↑a) (↑b)

noncomputable def toConcreteBTF0 : GF(2) → ConcreteBTField 0 :=
  fun x => if decide (x = 0) then zero else one

def last_nonzero (p : UniPoly R) : Option (Fin p.size) :=
  p.findIdxRev? (· != 0)

@[reducible, inline, specialize]
def messages (transcript : FullTranscript pSpec) (i : MessageIdx pSpec) :=
  transcript i.val

input := id

def AlgebraTowerEquiv.toAlgEquivOverRight (e : AlgebraTowerEquiv A B) (i j : ι) (h : i ≤ j) :
  letI : Algebra (B i) (B j) :=

def computableBasisExplicit (k : ℕ) (i : Fin (2 ^ k)) : ConcreteBTField k :=
  (Finset.univ : Finset (Fin k)).prod fun j =>
    if Nat.getBit (n := i.val) (k := j.val) == 1 then
      concreteTowerAlgebraMap (j.val + 1) k (by admit /- proof elided -/
      ) (Z (j.val + 1))
    else
      1

noncomputable def qMap_total_fiber
    
      (i : Fin r) (steps : ℕ) (h_i_add_steps : i.val + steps < ℓ + 𝓡)
        (y : sDomain 𝔽q β h_ℓ_add_R_rate (i := ⟨i.val + steps, by admit /- proof elided -/
        ⟩)) :
    Fin (2 ^ steps) → sDomain 𝔽q β h_ℓ_add_R_rate i :=
  if h_steps : steps = 0 then by
    
    subst h_steps
    simp only [add_zero, Fin.eta] at y
    exact fun _ => y
  else by
    
    let basis_y := sDomain_basis 𝔽q β h_ℓ_add_R_rate (i := ⟨i+steps,by admit /- proof elided -/
    ⟩) (by admit /- proof elided -/
    )
    let y_coeffs : Fin (ℓ + 𝓡 - (↑i + steps)) →₀ 𝔽q := basis_y.repr y

def verifier : Verifier oSpec (StmtIn R × (∀ i, OStmtIn R deg i))
                              (StmtOut R × (∀ i, OStmtOut R deg i)) (pSpec R deg) where
  verify := fun ⟨target, oStmt⟩ transcript => do
    letI polyLE := transcript 0
    guard (∑ x ∈ (univ.map D), polyLE.val.eval x = target)
    letI chal := transcript 1
    pure ⟨⟨(oStmt ()).val.eval chal, chal⟩, fun _ => oStmt ()⟩

def duplexSpongeHybridOracle : OracleSpec pSpec.ChallengeIdx :=
  fun i =>
    ⟨StmtIn × ((j : pSpec.MessageIdx) → (j.1 < i.1) → Vector U (pSpec.Lₚᵢ j)),
    Vector U (pSpec.Lᵥᵢ i)⟩

OracleSpec.SubSpec in VCVio.OracleComp.Coercions.SubSpec

instance instST₁ : ∀ i, SelectableType ((⟨!v[.P_to_V], !v[R⦃≤ deg⦄[X]]⟩ ++ₚ !p[]).Challenge i) :=
  instSelectableTypeChallengeAppend

instance Vector.instFintype {α : Type*} {n : ℕ} [VCVCompatible α] : Fintype (Vector α n) :=
  Fintype.ofEquiv _ (Equiv.rootVectorEquivFin).symm

def SkeletonNodeIndex.parent {s : Skeleton} (idx : SkeletonNodeIndex s) :
    Option (SkeletonNodeIndex s) :=
  match idx with
  | SkeletonNodeIndex.ofLeaf => none
  | SkeletonNodeIndex.ofInternal => none
  | SkeletonNodeIndex.ofLeft (.ofLeaf) => some .ofInternal
  | SkeletonNodeIndex.ofLeft (.ofInternal) => some .ofInternal
  | SkeletonNodeIndex.ofLeft idxLeft =>
    idxLeft.parent.map (SkeletonNodeIndex.ofLeft)
  | SkeletonNodeIndex.ofRight (.ofLeaf) => some .ofInternal
  | SkeletonNodeIndex.ofRight (.ofInternal) => some .ofInternal
  | SkeletonNodeIndex.ofRight idxRight =>
    idxRight.parent.map (SkeletonNodeIndex.ofRight)

hash_in_trace : (stmt, (Vector.drop inputState[0] SpongeSize.R)) ∈ trace.getQ (.inl ())

noncomputable def Bstar (x : ℝ) : ℝ := x.sqrt

def ζ (R : F[X][X][Y]) (x₀ : F) (H : F[X][Y]) [H_irreducible : Fact (Irreducible H)] : 𝕃 H :=
  let W  : 𝕃 H := liftToFunctionField (H.leadingCoeff);
  let T : 𝕃 H := liftToFunctionField (Polynomial.X);
    Polynomial.eval₂ liftToFunctionField (T / W)
      (Bivariate.evalX (Polynomial.C x₀) R.derivative)

Sum.inl in Init.Core

@[reducible, inline, specialize, simp]
def Challenge (pSpec : ProtocolSpec n) (i : ChallengeIdx pSpec) := pSpec.«Type» i.val

Equiv.ofBijective in Mathlib.Logic.Equiv.Defs

def eqTilde {L : Type} [CommRing L] {ℓ : ℕ} (r r' : Fin ℓ → L) : L :=
  MvPolynomial.eval r' (MvPolynomial.eqPolynomial r)

noncomputable instance {v : ι → F} {s : AffineSubspace F (ι → F)} [Fintype s] :
    Fintype (v +ᵥ s) := Fintype.ofFinite ↥(v +ᵥ s)

Nat.digits in Mathlib.Data.Nat.Digits.Defs

def HList.toDVec (l : HList) : DVec (m := Fin l.length) (fun i => l[i].1) := fun i => l[i].2

hℓ_bound : ∀ i : Fin (M + 1), ∀ j : Fin ((P.foldingParam i) + 1),
    Fintype.card (Gen_α i j).parℓ = 2
  hℓ_bound' : ∀ i : Fin (M + 1), ∀ j : Fin ((P.foldingParam i) + 1),
    Fintype.card (parℓ_type i j) = 2

receiveChallenge
  | ⟨0, _⟩ => fun ⟨⟨chals, o⟩, p⟩ => pure <|
    fun (α : F) =>
      ⟨
        ⟨Fin.append chals (fun (_ : Fin 1) => α), o⟩,
        ⟨p.1.foldNth (2 ^ (s i.castSucc).1) α, witness_lift p.2⟩
      ⟩
  | ⟨1, h⟩ => nomatch h

@[app_unexpander Fin.fcons₂]
def fcons₂Unexpander : Lean.PrettyPrinter.Unexpander
  | `($_ $a !h⦃$F⦄⟨$α₁⟩⟨$α₂⟩[$b, $bs,*]) => `(!h⦃$F⦄⟨$α₁⟩⟨$α₂⟩[$a, $b, $bs,*])
  | `($_ $a !h⦃$F⦄⟨$α₁⟩⟨$α₂⟩[$b]) => `(!h⦃$F⦄⟨$α₁⟩⟨$α₂⟩[$a, $b])
  | `($_ $a !h⦃$F⦄⟨$α₁⟩⟨$α₂⟩[]) => `(!h⦃$F⦄⟨$α₁⟩⟨$α₂⟩[$a])
  | _ => throw ()

Algebra.cast in Mathlib.Algebra.Algebra.Defs

FiniteDimensional in Mathlib.LinearAlgebra.FiniteDimensional.Defs

noncomputable def polyEvalLinearMap {L 𝔽q : Type*} [Field L] [Field 𝔽q] [Algebra 𝔽q L]
  (p : L[X]) (hp_add : IsLinearMap 𝔽q (fun x : L => p.eval x)) : L →ₗ[𝔽q] L :=
{
  toFun    := fun x => p.eval x,
  map_add' := hp_add.map_add,
  map_smul' := hp_add.map_smul
}

@[reducible]
def coreInteractionOracleReduction :=
  OracleReduction.append (oSpec:=[]ₒ)
    (Stmt₁ := Statement (L := L) (ℓ:=ℓ) (SumcheckBaseContext L ℓ) 0)
    (Stmt₂ := Statement (L := L) (ℓ:=ℓ) (SumcheckBaseContext L ℓ) (Fin.last ℓ))
    (Stmt₃ := FinalSumcheckStatementOut (L:=L) (ℓ:=ℓ))
    (Wit₁ := Witness (L := L) 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (ℓ:=ℓ) 0)
    (Wit₂ := Witness (L := L) 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (ℓ:=ℓ) (Fin.last ℓ))
    (Wit₃ := Unit)
    (OStmt₁ := OracleStatement 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) ϑ 0)
    (OStmt₂ := OracleStatement 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) ϑ (Fin.last ℓ))
    (OStmt₃ := OracleStatement 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) ϑ (Fin.last ℓ))
    (pSpec₁ := pSpecSumcheckFold 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate))
    (pSpec₂ := pSpecFinalSumcheckStep (L:=L))
    (R₁ := sumcheckFoldOracleReduction 𝔽q β (ϑ:=ϑ) (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (𝓑:=𝓑))
    (R₂ := finalSumcheckOracleReduction 𝔽q β (ϑ:=ϑ) (h_ℓ_add_R_rate := h_ℓ_add_R_rate))

class IsKnowledgeSound (relIn : Set (StmtIn × WitIn)) (relOut : Set (StmtOut × WitOut))
    (verifier : Verifier oSpec StmtIn StmtOut pSpec) where
  knowledgeError : ℝ≥0
  is_knowledge_sound : knowledgeSoundness init impl relIn relOut verifier knowledgeError

ringChar in Mathlib.Algebra.CharP.Defs

toNat in Mathlib.Computability.Reduce

embed : ιₛₒ ↪ ιₛᵢ ⊕ pSpec.MessageIdx

hEq := by admit /- proof elided -/

def outputRelation :
    Set (((StmtOut R) × (∀ i, OStmtOut R deg i)) × Unit) :=
  { ⟨⟨⟨newTarget, chal⟩, oStmt⟩, _⟩ | (oStmt ()).1.eval chal = newTarget }

def natCast_succ {k : ℕ} (n : ℕ) : natCast (k:=k) (n + 1) = natCast (k:=k) n + 1 :=

permute_or_inv_in_trace : ∀ i : Fin outputState.length,
    (inputState[i], outputState[i]) ∈ trace.getQ (.inr .Fwd)
    ∨ (outputState[i], inputState[i]) ∈ trace.getQ (.inr .Bwd)

@[inline] def lt [Zero T] [ToNat T] (a b : Cayley T) : Prop :=
  (↑a : Nat) < (↑b : Nat)

@[simp]
abbrev Witness.AfterSecondSumcheck : Type := Unit

def rbrSoundness (langIn : Set StmtIn) (langOut : Set StmtOut)
    (verifier : Verifier oSpec StmtIn StmtOut pSpec)
    (rbrSoundnessError : pSpec.ChallengeIdx → ℝ≥0) : Prop :=
  ∃ stateFunction : verifier.StateFunction init impl langIn langOut,
  ∀ stmtIn ∉ langIn,
  ∀ WitIn WitOut : Type,
  ∀ witIn : WitIn,
  ∀ prover : Prover oSpec StmtIn WitIn StmtOut WitOut pSpec,
  ∀ i : pSpec.ChallengeIdx,
    [fun ⟨transcript, challenge⟩ =>
      ¬ stateFunction i.1.castSucc stmtIn transcript ∧
        stateFunction i.1.succ stmtIn (transcript.concat challenge)
    | do
      (simulateQ (impl ++ₛₒ challengeQueryImpl : QueryImpl _ (StateT σ ProbComp))
        (do
          let ⟨transcript, _⟩ ← prover.runToRound i.1.castSucc stmtIn witIn
          let challenge ← liftComp (pSpec.getChallenge i) _
          return (transcript, challenge))).run' (← init)] ≤
      rbrSoundnessError i

def canonical (p : UniPoly R) := p.trim = p

noncomputable instance {v : ι → F} {s : AffineSubspace F (ι → F)} [inst : Nonempty s] :
    Nonempty (v +ᵥ s) :=

GaloisField in Mathlib.FieldTheory.Finite.GaloisField

PFunctor.Lens.id in ToMathlib.PFunctor.Lens.Basic

Cardinal in Mathlib.SetTheory.Cardinal.Defs

@[inline, reducible]
protected def id :
    Witness.Lens OuterStmtIn OuterStmtOut OuterWitIn OuterWitOut OuterWitIn OuterWitOut :=
  ⟨Prod.snd, fun _ => Prod.snd⟩

@[reducible, inline]
def 𝕫 {R} {sz} (stmt : Statement R sz) (wit : Witness R sz) : Fin sz.n → R :=
  Fin.append stmt wit ∘ Fin.cast (by admit /- proof elided -/
  )

verify : StmtIn → pSpec.Challenges →
    OracleComp (oSpec ++ₒ ([OStmtIn]ₒ ++ₒ [pSpec.Message]ₒ)) StmtOut

def AlgebraTowerEquiv.algebraMapRightUp (e : AlgebraTowerEquiv A B) (i j : ι)
    (h : i ≤ j) : (A i) →+* (B j) :=

alias d2SQueryImpl := duplexSpongeToBasicFSQueryImpl

def rightpad {m : ℕ} {α : Sort*} (n : ℕ) (a : α) (v : Fin m → α) : Fin n → α :=
  fun i => if h : i < m then v ⟨i, h⟩ else a

@[reducible, simp] def StmtIn : Type := R

def foldKnowledgeError (i : Fin ℓ) (_ : (pSpecFold (L := L)).ChallengeIdx) : ℝ≥0 :=
  let err_SC := (1 : ℝ≥0) / (Fintype.card L)
  
  let err_BE := if hi : ϑ ∣ (i.val + 1) then
    
    ϑ * (Fintype.card ((sDomain 𝔽q β h_ℓ_add_R_rate)
      ⟨i.val + 1, by admit /- proof elided -/
        ⟩) : ℝ≥0) / (Fintype.card L)
  else 0
  err_SC + err_BE

def SkeletonNodeIndex.leftChild {s : Skeleton} (idx : SkeletonNodeIndex s) :
    Option (SkeletonNodeIndex s) :=
  match idx with
  | SkeletonNodeIndex.ofLeaf => none
  | @SkeletonNodeIndex.ofInternal left right =>
    some (SkeletonNodeIndex.ofLeft (getRootIndex left))
  | SkeletonNodeIndex.ofLeft idxLeft =>
    idxLeft.leftChild.map (SkeletonNodeIndex.ofLeft)
  | SkeletonNodeIndex.ofRight idxRight =>
    idxRight.leftChild.map (SkeletonNodeIndex.ofRight)

instance [Zero T] [ToNat T] : LT (Cayley T) where
  lt := lt

def accepts (x : Fin numWires → 𝓡) (g : Gate 𝓡 numWires) : Prop :=
  g.eval x = 0

private def f (x : ℚ) : ℚ := x^2 - x

def findImports (path : System.FilePath) : IO (Array Lean.Name) := do
  return (← Lean.parseImports' (← IO.FS.readFile path) path.toString)
    |>.map (fun imp ↦ imp.module) |>.erase `Init

def Polynomial.toImpl {R : Type*} [Semiring R] (p : R[X]) : UniPoly R :=
  match p.degree with
  | ⊥ => #[]
  | some d  => .ofFn (fun i : Fin (d + 1) => p.coeff i)

@[reducible, simp] def StmtOut := Query OStatement

@[reducible]
def OracleStatement (i : Fin (k + 1)) : Fin (i.val + 1) → Type :=
  fun j =>
    evalDomain D x (∑ j' ∈ finRangeTo j.1, s j')
      → F

def aeval {A : Type w} [CommSemiring A] [Algebra R A] (s : A) : P →ₐ[R] A :=
  eval₂AlgHom (Algebra.ofId R A) s

def canonicalEmbedding (k : ℕ) : BTField k →+* BTField (k+1) :=
  AdjoinRoot.of (poly k)

def toEvalsZeroOne (p : MvPolynomial σ R) : (σ → Fin 2) → R :=
  fun x => eval (x : σ → R) p

for _ in [0:s] do
      x := (x * x) % n
      if x == n - 1 ∨ x ≤ 1 then
        break
    if x ≠ n - 1 then
      return false

def listDecodable (C : Code ι F) (r : ℝ) (ℓ : ℝ) : Prop :=
  ∀ y : ι → F, listOfCloseCodewordsRel C y r ≤ ℓ

@[simp]
def poly (k : ℕ) : Polynomial (BTField k) := definingPoly (s:=(Z k))

instance {ι : Type u} (v : ι → Type v) [O : ∀ i, OracleInterface (v i)]
    [h : ∀ i, Fintype (Response (v i))]
    [h' : ∀ i, Inhabited (Response (v i))] :
    [v]ₒ.FiniteRange where
  range_fintype' := h
  range_inhabited' := h'

input := fun i => ⟨i.1.2, i.2⟩

def renameMessage (pSpec : ProtocolSpec n) (NewMessage : pSpec.MessageIdx → Type) :
    ProtocolSpec n :=
  ⟨ pSpec.dir,
    fun i => if h : pSpec.dir i = Direction.P_to_V then NewMessage ⟨i, h⟩ else pSpec.«Type» i⟩

instance : Unique (Fin 0 → α) where
  uniq v := by admit /- proof elided -/

def backTrack (trace : QueryLog (duplexSpongeChallengeOracle StmtIn U))
    (state : CanonicalSpongeState U) :
    OptionT Option ((StmtIn × (i : Fin (n + 1)) × (pSpec.MessagesUpTo i))) :=
  sorry

def deriveTranscriptDSFSAux {ι : Type} {oSpec : OracleSpec ι} {StmtIn : Type}
    (sponge : CanonicalDuplexSponge U)
    (messages : pSpec.Messages) (i : Fin (n + 1)) :
      OracleComp (oSpec ++ₒ duplexSpongeChallengeOracle StmtIn U)
        (CanonicalDuplexSponge U × pSpec.Transcript i) :=
  Fin.induction
    (pure (sponge, fun i => i.elim0))
    (fun i ih => do
      let ⟨curSponge, prevTranscript⟩ ← ih
      match hDir : pSpec.dir i with
      | .V_to_P =>
        let ⟨challenge, newSponge⟩ ← liftM (curSponge.squeeze (challengeSize ⟨i, hDir⟩))
        let deserializedChallenge : pSpec.Challenge ⟨i, hDir⟩ :=
          Deserialize.deserialize challenge
        return (newSponge, prevTranscript.concat deserializedChallenge)
      | .P_to_V =>
        let serializedMessage : Vector U (messageSize ⟨i, hDir⟩) :=
          Serialize.serialize (messages ⟨i, hDir⟩)
        let newSponge ← liftM (DuplexSponge.absorb curSponge serializedMessage.toList)
        return (newSponge, prevTranscript.concat (messages ⟨i, hDir⟩)))
    i

def computableNTTStage [Fact (LinearIndependent 𝔽q β)]
  (i : Fin ℓ) (b : Fin (2 ^ (ℓ + R_rate)) → L) : Fin (2^(ℓ + R_rate)) → L :=
  have h_2_pow_i_lt_2_pow_ℓ_add_R_rate: 2^i.val < 2^(ℓ + R_rate) := by admit /- proof elided -/

def fappend₂ {A : Sort u} {B : Sort v} {F : A → B → Sort w} {m n : ℕ}
    {α₁ : Fin m → A} {β₁ : Fin n → A} {α₂ : Fin m → B} {β₂ : Fin n → B}
    (u : (i : Fin m) → F (α₁ i) (α₂ i)) (v : (i : Fin n) → F (β₁ i) (β₂ i)) :
    (i : Fin (m + n)) → F (Fin.vappend α₁ β₁ i) (Fin.vappend α₂ β₂ i) :=
  match n with
  | 0 => u
  | k + 1 => fconcat₂ (fappend₂ u (fun i => v (Fin.castSucc i))) (v (Fin.last k))

@[simp]
def extractorLens (i : Fin n) : Extractor.Lens
    (StatementRound R n i.castSucc × (∀ i, OracleStatement R n deg i))
    (StatementRound R n i.succ × (∀ i, OracleStatement R n deg i))
    (Simple.StmtIn R × (∀ i, Simple.OStmtIn R deg i))
    (Simple.StmtOut R × (∀ i, Simple.OStmtOut R deg i))
    Unit Unit Unit Unit where
  stmt := oStmtLens R n deg D i
  wit := Witness.InvLens.trivial

instance instEquivalenceEquiv : Equivalence (equiv (R := R)) where
  refl := equiv_refl
  symm := equiv_symm
  trans := equiv_trans

example : NestedList 0 = Nat := rfl
example (n : ℕ) : NestedList (n + 1) = List (NestedList n) := rfl

noncomputable def canonicalRepOf𝒪 {H : F[X][Y]} (β : 𝒪 H) : F[X][Y] :=
  Polynomial.modByMonic β.out (H_tilde' H)

proj_knowledgeSound : ∀ outerStmtIn innerStmtOut outerWitOut,
    compatStmt outerStmtIn innerStmtOut →
    (lens.stmt.lift outerStmtIn innerStmtOut, outerWitOut) ∈ outerRelOut →
    (innerStmtOut, lens.wit.proj (outerStmtIn, outerWitOut)) ∈ innerRelOut

structure InterleavedCode (κ ι : Type*) [Fintype κ] [Fintype ι] (F : Type*) [Semiring F] where
  MF : MatrixSubmodule κ ι F
  LC : LinearCode ι F

structure Context.Lens (OuterStmtIn OuterStmtOut InnerStmtIn InnerStmtOut
                          OuterWitIn OuterWitOut InnerWitIn InnerWitOut : Type) where
  stmt : Statement.Lens OuterStmtIn OuterStmtOut InnerStmtIn InnerStmtOut
  wit : Witness.Lens OuterStmtIn InnerStmtOut OuterWitIn OuterWitOut InnerWitIn InnerWitOut

@[inline]
def zsmul [SMul ℤ R] (m : ℤ) (p : MlPolyEval R n) : MlPolyEval R n := p.map (fun a => m • a)

structure ParamConditions (P : Params ι F) where
  h_deg : ∃ k : ℕ, P.deg = 2^k
  h_foldingParams : ∀ i : Fin (M + 1), ∃ k : ℕ, (P.foldingParam i) = 2^k
  h_deg_ge : P.deg ≥ ∏ i : Fin (M + 1), (P.foldingParam i)
  h_smooth : ∀ i : Fin (M + 1), Smooth (P.φ i)
  h_smooth_le : ∀ i : Fin (M + 1), Fintype.card (ι i) ≤ (degree ι P i)
  h_repeatP_le : ∀ i : Fin (M + 1), P.repeatParam i + 1 ≤ (degree ι P i)

@[reducible]
def GroupDecodeOracle : OracleSpec Unit := fun _ => (BitVec bitLength × ι, Unit)

abbrev Fwd : PermuteDir := Sum.inl ()

instance : ∀ i, SelectableType ((pSpecNonLastBlocks 𝔽q β (ϑ:=ϑ)
  (h_ℓ_add_R_rate := h_ℓ_add_R_rate)).Challenge i) := instSelectableTypeChallengeSeqCompose

def churchRec {α : Type} (n : ChurchNat α) (step : α → α) (base : α) : α :=
  n step base

sendMessage
  | ⟨0, h⟩ => nomatch h
  | ⟨1, _⟩ => fun ⟨⟨chals, o⟩, p⟩ =>
    pure ⟨fun x => p.1, ⟨⟨chals, o⟩, p⟩⟩

noncomputable def errorBound (δ : ℝ≥0) (deg : ℕ) (domain : ι ↪ F) : ℝ≥0 :=
  letI ρ : ℝ≥0 := ρ (ReedSolomon.code domain deg)
  if δ ∈ Set.Ioc 0 ((1 - ρ)/2)
  then Fintype.card ι / Fintype.card F
  else if δ ∈ Set.Ioo ((1 - ρ)/2) (1 - ρ.sqrt)
       then letI m := min (1 - ρ.sqrt - δ) (ρ.sqrt / 20)
            ⟨(deg ^ 2 : ℝ≥0) / ((2 * m) ^ 7 * (Fintype.card F : ℝ)), by admit /- proof elided -/
            ⟩
       else 0

def toOracleSpec {ι : Type u} (v : ι → Type v) [O : ∀ i, OracleInterface (v i)] :
    OracleSpec ι := fun i => ((O i).Query, (O i).Response)

Fin.subNat in Init.Data.Fin.Basic

@[inline] def sub [Zero T] [ToNat T] (a b : Cayley T) : Cayley T :=
  subNat a ↑b

def inputRelation : Set ((StmtIn R × (∀ i, OStmtIn R deg i)) × Unit) :=
  { ⟨⟨target, oStmt⟩, _⟩ | ∑ x ∈ (univ.map D), (oStmt ()).1.eval x = target }

class HasSize (α : Type*) (β : Type*) where
  size : Nat
  toFun : α ↪ Vector β size

Polynomial.eval₂ in Mathlib.Algebra.Polynomial.Eval.Defs

def generateSrs (n : ℕ) (a : ZMod p) : Vector G₁ (n + 1) × Vector G₂ 2 :=
  (towerOfExponents g₁ a n, towerOfExponents g₂ a 1)

def liftF (f : Fin n → α) : ℕ → α :=
  fun m ↦ if h : m < n then f ⟨m, h⟩ else 0

def srSoundnessGame (P : Prover.StateRestoration.Soundness oSpec StmtIn pSpec) :
    OracleComp (oSpec ++ₒ (srChallengeOracle StmtIn pSpec))
      (pSpec.FullTranscript × StmtIn) := do
  let ⟨stmtIn, messages⟩ ← P
  let transcript ← messages.deriveTranscriptSR stmtIn
  return ⟨transcript, stmtIn⟩

sendMessage
  | ⟨0, h⟩ => nomatch h

@[reducible]
def ROspec (α β γ : Type) : OracleSpec Unit := fun _ => (α × β, γ)

noncomputable instance {s : Set (ι → F)} : Fintype (affineSpan F s) :=
  Fintype.ofFinite ↥(affineSpan F s)

structure BerlekampWelchCondition (e k : ℕ) (ωs f : Fin n → F) (E Q : Polynomial F) : Prop where
  cond: ∀ i : Fin n, Q.eval (ωs i) = (f i) * E.eval (ωs i)
  E_natDegree : E.natDegree = e
  E_leadingCoeff : E.coeff e = 1
  Q_natDegree : Q.natDegree ≤ e + k - 1

def sumcheckFoldKnowledgeError := fun j : (pSpecSumcheckFold 𝔽q β (ϑ:=ϑ)
    (h_ℓ_add_R_rate := h_ℓ_add_R_rate)).ChallengeIdx =>
    if hj: (j.val % NBlockMessages (ϑ:=ϑ)) % 2 = 1 then
      foldKnowledgeError 𝔽q β (ϑ:=ϑ) (h_ℓ_add_R_rate := h_ℓ_add_R_rate)
        ⟨j / NBlockMessages (ϑ:=ϑ) * ϑ + ((j % NBlockMessages (ϑ:=ϑ)) / 2 + 1), by admit /- proof elided -/
        ⟩ ⟨1, rfl⟩
    else 0

instance : Add (Cayley T) where
  add := add

class SliceGE (coll : Type u) (start : Type v) (valid : outParam (coll → start → Prop))
    (subcoll : outParam ((xs : coll) → (start : start) → (h : valid xs start) → Type w)) where
  sliceGE : (xs : coll) → (start : start) → (h : valid xs start) → subcoll xs start h

def AlgebraTowerEquiv.algebraMapLeftUp (e : AlgebraTowerEquiv A B) (i j : ι)
    (h : i ≤ j) : (B i) →+* (A j) :=

Ideal.span in Mathlib.RingTheory.Ideal.Span

BStar : ∀ i : Fin (M + 1), ∀ j : Fin ((P.foldingParam i) + 1),
    (Set ((indexPowT (S i) (P.φ i) j) → F)) → Type → ℝ≥0
  errStar : ∀ i : Fin (M + 1), ∀ j : Fin ((P.foldingParam i) + 1),
    (Set ((indexPowT (S i) (P.φ i) j) → F)) → Type → ℝ → ENNReal

hδLe : ∀ i : Fin (M + 1),
    (δ i) ≤ 1 - Finset.univ.sup (fun j => BStar i j (C i j) (Gen_α i j).parℓ)

def JohnsonDenominator (B : Finset (Fin n → F)) (v : Fin n → F) : ℚ :=
  let e := e B v
  let d := d B
  let q : ℚ := Fintype.card F
  let frac := q / (q - 1)
  (1- frac * e/n) ^ 2 - (1 - frac * d/n)

def ofFlatten {m n : ℕ} (v : Vector α (m * n)) : Matrix α m n :=
  (Vector.finRange m).map (fun i => (v.extract (i.val * n) (i.val * n + n)).cast
    (by admit /- proof elided -/
      ))

Fin.succAbove in Mathlib.Data.Fin.SuccPred

noncomputable def ElocPolyF (ωs f : Fin n → F) (p : Polynomial F) : Polynomial F :=
  ElocPoly n (liftF ωs) (liftF f) p

orderOf in Mathlib.GroupTheory.OrderOfElement

def reduction (i : Fin n) : Reduction oSpec
    ((StatementRound R n i.castSucc) × (∀ i, OracleStatement R n deg i)) Unit
    ((StatementRound R n i.succ) × (∀ i, OracleStatement R n deg i)) Unit (pSpec R deg) :=
  (Simple.reduction R deg D oSpec).liftContext (oCtxLens R n deg D i).toContext

instance : DFunLike F α β where
  coe := DFunEquiv.equiv.toFun
  coe_injective' := DFunEquiv.equiv.injective

instance : Unique (FullTranscript (default : ProtocolSpec 0)) := inferInstance

def ar2 (k0 k1 : ℕ) : Fin 2 → ℕ
  | ⟨0, _⟩ => k0
  | ⟨1, _⟩ => k1

def FinalSumcheckWit := fun (m : Fin (1 + 1)) =>
 match m with
 | ⟨0, _⟩ => Witness (L := L) 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (Fin.last ℓ)
 | ⟨1, _⟩ => Unit

def isCompliant (i : Fin (ℓ)) (steps : ℕ) [NeZero steps]
  (h_i_add_steps : i + steps ≤ ℓ)
  (f_i : OracleFunction 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) ⟨i, by admit /- proof elided -/
  ⟩)
  (f_i_plus_steps : OracleFunction 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate)
      ⟨i + steps, by admit /- proof elided -/
      ⟩)
  (challenges : Fin steps → L) : Prop :=
  ∃ (h_fw_dist_lt : 2 * fiberwiseDistance 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (i := i)
      (steps := steps) h_i_add_steps f_i < (BBF_CodeDistance ℓ 𝓡 ⟨i + steps, by admit /- proof elided -/
      ⟩ : ℕ∞))
    (h_dist_next_lt : 2 * distFromCode f_i_plus_steps
      (BBF_Code 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate) ⟨i + steps, by admit /- proof elided -/
      ⟩)
      < (BBF_CodeDistance ℓ 𝓡 ⟨i + steps, by admit /- proof elided -/
      ⟩ : ℕ∞)), 
    
    let h_dist_curr_lt := fiberwise_dist_lt_imp_dist_lt_unique_decoding_radius 𝔽q β
      (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (i := i) steps h_i_add_steps f_i
      (h_fw_dist_lt := h_fw_dist_lt)
    let f_bar_i := uniqueClosestCodeword 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate)
      (i := ⟨i, by admit /- proof elided -/
      ⟩) (h_i := fin_ℓ_lt_ℓ_add_R i) f_i h_dist_curr_lt
    let f_bar_i_plus_steps := uniqueClosestCodeword 𝔽q β
      (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (i := ⟨i + steps, by admit /- proof elided -/
      ⟩)
      (h_i := fin_ℓ_steps_lt_ℓ_add_R i steps h_i_add_steps)
      f_i_plus_steps h_dist_next_lt
    iterated_fold 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate)
      (steps := ⟨steps, by admit /- proof elided -/
      ⟩)
      (i := ⟨i, by admit /- proof elided -/
      ⟩)
      (h_i_add_steps := by admit /- proof elided -/
      )
      f_bar_i challenges = f_bar_i_plus_steps

@[inline, reducible]
def Witness.InvLens (OuterStmtIn OuterWitIn OuterWitOut InnerWitIn InnerWitOut : Type)
    := PFunctor.Lens ((OuterStmtIn × OuterWitOut) X^ OuterWitIn)
                     (InnerWitOut X^ InnerWitIn)

Set.toFinset in Mathlib.Data.Fintype.Sets

instance instDCastPSigma : DCast ((a : α) ×' β a) (fun a => γ a.1 a.2) where
  dcast hab c := dcast₂ (by admit /- proof elided -/
  ) (by admit /- proof elided -/
  ) c
  dcast_id := by admit /- proof elided -/

instance : NatCast (UniPoly R) := ⟨fun n => UniPoly.C (n : R)⟩

def sBasis (i : Fin r) (h_i : i < ℓ + R_rate) : Fin (ℓ + R_rate - i) → L :=
  fun k => β ⟨i + k.val, by admit /- proof elided -/
  ⟩

def inputRelation (cond : ∑ i, (s i).1 ≤ n) [DecidableEq F] (δ : ℝ≥0) :
    Set
      (
        (
          Statement F (Fin.last k) ×
          (∀ j, OracleStatement D x s (Fin.last k) j)
        ) ×
        Witness F s d (Fin.last k).castSucc
      ) := sorry

Set.Pairwise in Mathlib.Logic.Pairwise

def powFiberT (i : ℕ) {k : ℕ} {S : Finset ι} {φ : ι ↪ F} (S' : Finset (indexPowT S φ i))
  (φ' : (indexPowT S φ i) ↪ F) (y : indexPowT S φ k) :=
  { x : (indexPowT S φ i) // x ∈ S' ∧ (φ' x) ^ (2^(k-i)) = y.val }

Mul in Init.Prelude

def divNat [Zero T] [DecidableEq T] [ToNat T]
    (dividend divisor : Cayley T) : Nat → Cayley T
  | 0        => zero  
  | .succ fuel =>
    
    if (↑divisor : Nat) = 0 then
      zero
    else
      
      if (↑divisor : Nat) ≤ (↑dividend : Nat) then
        
        add one (divNat (sub dividend divisor) divisor fuel)
      else
        zero

instance : DFunEquiv (∀ a : α, β a) α β where
  equiv := Equiv.refl _

ratchetUnchecked : α → α

@[simp]
instance Nontrivial (k : ℕ) : Nontrivial (BTField k) := inferInstance

@[reducible, inline, specialize]
def MessagesUpTo (k : Fin (n + 1)) (pSpec : ProtocolSpec n) : Type :=
  ∀ i, pSpec.MessageUpTo k i

Repr in Init.Data.Repr
</all_available_defs>

<all_available_lemmas>
BitVec.xor_self in Init.Data.BitVec.Lemmas
BitVec.eq_zero_or_eq_one in Init.Data.BitVec.Lemmas
BitVec.xor_eq_zero_iff in Init.Data.BitVec.Lemmas
if_neg in Init.Core
ne_eq in Init.SimpLemmas
not_false_eq_true in Init.SimpLemmas
one_ne_zero in Mathlib.Algebra.NeZero

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]

lemma getBit_of_and {n m k: ℕ} : getBit k (n &&& m) = getBit k n &&& getBit k m

lemma and_eq_zero_iff_and_each_getBit_eq_zero {n m : ℕ} :
    n &&& m = 0 ↔ ∀ k, Nat.getBit k n &&& Nat.getBit k m = 0

@[simp]
lemma Fintype.zero_lt_card {ι : Type*} [Fintype ι] [Nonempty ι] : 0 < Fintype.card ι

theorem BitVec.dcast_bitvec_eq {l r val : ℕ} (h_width_eq : l = r) :
    dcast h_width_eq (BitVec.ofNat l val) = BitVec.ofNat r val

theorem cast_Type_idx_symm {hn} (hSpec : pSpec₁.cast hn = pSpec₂) {i : Fin n₂} :
    pSpec₁.«Type» (Fin.cast hn.symm i) = pSpec₂.«Type» i

lemma add_eq_zero_iff_eq {k : ℕ} (a b : ConcreteBTField k) : a + b = 0 ↔ a = b

@[simp]
theorem cast_perfectCompleteness (hComplete : R.perfectCompleteness init impl relIn relOut) :
    (R.cast hn hSpec hOₘ).perfectCompleteness init impl relIn relOut

theorem ext_hcons {β : Fin n → Sort u} (a₁ a₂ : α) (v₁ v₂ : (i : Fin n) → β i) :
    hcons a₁ v₁ = hcons a₂ v₂ ↔ a₁ = a₂ ∧ v₁ = v₂

theorem peval_eq_eval_sumToIter_rename (f : σ → σ₁ ⊕ σ₂) (x : σ₁ → R) (p : MvPolynomial σ R) :
    peval f x p = eval (C ∘ x) (sumToIter R σ₁ σ₂ (rename f p))

theorem Reduction.run_of_prover_first [ProverOnly pSpec] (stmt : StmtIn) (wit : WitIn)
    (reduction : Reduction oSpec StmtIn WitIn StmtOut WitOut pSpec) :
      reduction.run stmt wit = (do
        let state := reduction.prover.input (stmt, wit)
        let ⟨msg, state⟩ ← liftComp (reduction.prover.sendMessage ⟨0, by simp⟩ state) _
        let ctxOut ← reduction.prover.output state
        let transcript : pSpec.FullTranscript := fun i => match i with | ⟨0, _⟩ => msg
        let stmtOut ← reduction.verifier.verify stmt transcript
        return (⟨transcript, ctxOut⟩, stmtOut))

omit Oₘ in
theorem seqCompose_completeness (hInit : init.neverFails)
    (rel : (i : Fin (m + 1)) → Set (Stmt i × Wit i))
    (R : ∀ i, Reduction oSpec (Stmt i.castSucc) (Wit i.castSucc) (Stmt i.succ) (Wit i.succ)
      (pSpec i))
    (completenessError : Fin m → ℝ≥0)
    (h : ∀ i, (R i).completeness init impl (rel i.castSucc) (rel i.succ) (completenessError i)) :
      (Reduction.seqCompose Stmt Wit R).completeness init impl (rel 0) (rel (Fin.last m))
        (∑ i, completenessError i)

lemma concrete_mul_zero
  (prevBTFieldProps : ConcreteBTFieldProps (k := k - 1))
  (a : ConcreteBTField k) : concrete_mul a (zero (k:=k)) = zero (k:=k)

theorem FullData.toLeafData_rightSubtree {α} {s_left s_right : Skeleton}
    (tree : FullData α (Skeleton.internal s_left s_right)) :
    tree.toLeafData.rightSubtree =
      tree.rightSubtree.toLeafData

@[simp]
theorem fflatten₂_two_eq_append {A : Sort u} {B : Sort v} {F : A → B → Sort w} {n : Fin 2 → ℕ}
    {α : (i : Fin 2) → (j : Fin (n i)) → A}
    {β : (i : Fin 2) → (j : Fin (n i)) → B}
    {v : (i : Fin 2) → (j : Fin (n i)) → F (α i j) (β i j)} :
    fflatten₂ v = fappend₂ (F := F) (v 0) (v 1)

@[simp]
protected lemma elocPoly_ne_zero : ElocPoly n ωs f p ≠ 0

lemma dappend_right_of_not_lt {motive : Fin (m + n) → Sort u}
    (u : (i : Fin m) → motive (castAdd n i)) (v : (i : Fin n) → motive (natAdd m i))
    (i : Fin (m + n)) (h : ¬ i.val < m) :
      dappend (motive := motive) u v i = dcast (by ext; simp; omega) (v ⟨i - m, by omega⟩)

theorem cast_eq_cast_iff {α β γ : Sort u} {h : α = γ} {h' : β = γ} {a : α} {b : β} :
    cast h a = cast h' b ↔ a = cast (h'.trans h.symm) b

@[simp]
theorem dist_le_card (C : Set (n → R)) : dist C ≤ Fintype.card n

@[simp]
theorem OracleReduction.run_eq_run_reduction [∀ i, OracleInterface (pSpec.Message i)]
    {stmt : StmtIn} {oStmt : ∀ i, OStmtIn i} {wit : WitIn}
    {oracleReduction : OracleReduction oSpec StmtIn OStmtIn WitIn StmtOut OStmtOut WitOut pSpec} :
      oracleReduction.run stmt oStmt wit =
        oracleReduction.toReduction.run ⟨stmt, oStmt⟩ wit

omit h_Fq_char_prime hF₂ in
lemma inductive_rec_form_W_comp (i : Fin r) (h_i_add_1 : i + 1 < r)
    (h_prev_linear_map : IsLinearMap (R := 𝔽q) (M := L[X]) (M₂ := L[X])
      (f := fun inner_p ↦ (W 𝔽q β i).comp inner_p))
    : ∀ p: L[X], (W 𝔽q β (i + 1)).comp p =
      ((W 𝔽q β i).comp p) ^ Fintype.card 𝔽q -
        C (eval (β i) (W 𝔽q β i)) ^ (Fintype.card 𝔽q - 1) * ((W 𝔽q β i).comp p)

@[grind =]
theorem monomialXY_eq_monomialXY_iff {n m p q : ℕ} {a b : F} :
  monomialXY n m a = monomialXY p q b ↔ n = p ∧ m = q ∧ a = b ∨ a = 0 ∧ b = 0

theorem reduction_perfectCompleteness (hInit : init.neverFails) :
    (reduction R n deg D oSpec i).perfectCompleteness init impl
    (relationRound R n deg D i.castSucc) (relationRound R n deg D i.succ)

lemma getLowBits_joinBits {n m : ℕ} (low : Fin (2 ^ n)) (high : Fin (2 ^ m)) :
  getLowBits n (joinBits low high).val = low.val

@[simp]
theorem OracleVerifier.id_soundness {lang : Set (StmtIn × ∀ i, OStmtIn i)} :
    (OracleVerifier.id : OracleVerifier oSpec _ _ _ _ _).soundness
      init impl lang lang 0

@[simp]
theorem init_update_last : init (update s (Fin.last n) y) = init s

theorem linear_sum_repr (R : Type*) [CommRing R] (S : Type*) [CommRing S] [Algebra R S]
    (pb : PowerBasis R S) (h_dim : pb.dim = (2 : ℕ)) (s : S) :
    ∃ a b : R, s = a • pb.gen + algebraMap R S b

@[simp] lemma extract_dir : pSpec⟦start:stop⟧.dir = pSpec.dir⟦start:stop⟧

lemma aeval_eq' {A : Type y} [CommSemiring A] [Algebra R A] {F : Type z} [FunEquiv F σ A]
    (f : P →ₐ[R] A) (p : P) : f p = aeval (fun s => f (X s) : F) p

theorem join_of_split {k : ℕ} (h_pos : k > 0) (x : ConcreteBTField k)
    (hi_btf lo_btf : ConcreteBTField (k - 1))
    (h_split_eq : split h_pos x = (hi_btf, lo_btf)) :
    x = 《 hi_btf, lo_btf 》

@[simp]
theorem distanceLE_polynomial_degreeLT : distanceLE (R⦃< d⦄[X]) (d - 1)

lemma shift_left_def {s : Finset ℕ} :
    shift_left s = s.filterMap
    (fun n => match n with
      | 0 => .none
      | n + 1 => .some n
      )
    (by aesop)

theorem take_drop_append {α : Sort*} (m : ℕ) (h : m ≤ n) (v : Fin n → α) :
    Fin.append (take m h v) (drop m h v) = fun i => v (i.cast (by omega))

theorem prime_11 : Nat.Prime 11

lemma join_via_add_smul_one_zero_eq_Z {k : ℕ} (h_pos : k > 0) :
  ⋘ 1, 0 ⋙ = Z k

lemma βᵢ_not_in_Uᵢ (i : Fin r) :
    β i ∉ U 𝔽q β i

@[simp]
theorem insertNth_zero_zero : insertNth p 0 (0 : Fin n →₀ M) = 0

@[simp]
theorem verifier_first (pSpec : ProtocolSpec n) [NeZero n] [h : VerifierFirst pSpec] :
    pSpec.dir 0 = .V_to_P

theorem natDegree_finSuccEquivNth (f : MvPolynomial (Fin (n + 1)) R) :
    (finSuccEquivNth R p f).natDegree = degreeOf p f

theorem commitOracleVerifier_rbrKnowledgeSoundness (i : Fin ℓ)
    (hCR : isCommitmentRound ℓ ϑ i) :
    (commitOracleVerifier 𝔽q β (ϑ := ϑ) (h_ℓ_add_R_rate := h_ℓ_add_R_rate)
      i hCR).rbrKnowledgeSoundness init impl
      (relIn := foldStepRelOut (mp := mp) 𝔽q β (ϑ := ϑ)
        (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (𝓑 := 𝓑) i)
      (relOut := roundRelation (mp := mp) 𝔽q β (ϑ := ϑ)
        (h_ℓ_add_R_rate := h_ℓ_add_R_rate) (𝓑 := 𝓑) i.succ)
      (commitKnowledgeError 𝔽q β (h_ℓ_add_R_rate := h_ℓ_add_R_rate))

@[simp]
theorem OracleReduction.id_runWithLog (stmt : StmtIn) (oStmt : ∀ i, OStmtIn i) (wit : WitIn) :
    (OracleReduction.id : OracleReduction oSpec StmtIn OStmtIn WitIn _ _ _ _).runWithLog
      stmt oStmt wit = pure ⟨⟨default, ⟨stmt, oStmt⟩, wit⟩, ⟨stmt, oStmt⟩, [], []⟩

@[simp]
theorem vcons_of_one (a : α) {i : Fin 1} : !v[a] i = match i with

theorem range_vconcat {α : Type*} (v : Fin n → α) (a : α) :
    Set.range (vconcat v a) = insert a (Set.range v)

lemma card_le_card_of_count_inj {α β : Type*} [DecidableEq α] [DecidableEq β]
    {s : Multiset α} {s' : Multiset β}
  {f : α → β} (inj : Function.Injective f) (h : ∀ a : α, s.count a ≤ s'.count (f a)) :
  s.card ≤ s'.card

theorem join_eq_iff_dcast_extractLsb {k : ℕ} (h_pos : k > 0) (x : ConcreteBTField k)
  (hi_btf lo_btf : ConcreteBTField (k - 1)) :
  x = 《 hi_btf, lo_btf 》 ↔
  (hi_btf = dcast (h_sub_middle h_pos) (BitVec.extractLsb (hi := 2 ^ k - 1) (lo := 2 ^ (k - 1)) x) ∧
  lo_btf = dcast (h_middle_sub) (BitVec.extractLsb (hi := 2 ^ (k - 1) - 1) (lo := 0) x))

theorem dcast_eq_root_cast (h : a = a') : dcast h b = _root_.cast (congrArg β h) b

theorem seqCompose_knowledgeSoundness
    (rel : (i : Fin (m + 1)) → Set ((Stmt i × ∀ j, OStmt i j) × Wit i))
    (V : (i : Fin m) →
      OracleVerifier oSpec (Stmt i.castSucc) (OStmt i.castSucc) (Stmt i.succ) (OStmt i.succ)
        (pSpec i))
    (knowledgeError : Fin m → ℝ≥0)
    (h : ∀ i, (V i).knowledgeSoundness init impl (rel i.castSucc) (rel i.succ) (knowledgeError i)) :
      (OracleVerifier.seqCompose Stmt OStmt V).knowledgeSoundness
        init impl (rel 0) (rel (Fin.last m)) (∑ i, knowledgeError i)

lemma join_eq_join_iff (k : ℕ) (h_pos : k > 0) (hi₁ hi₀ lo₁ lo₀ : BTField (k - 1)) :
    ⋘ hi₁, lo₁ ⋙ = ⋘ hi₀, lo₀ ⋙ ↔
  hi₁ = hi₀ ∧ lo₁ = lo₀

theorem embedSum_succ {m : ℕ} {n : Fin (m + 1) → ℕ} {i : Fin (m + 1)} (j : Fin (n i)) :
    embedSum i j = (match i with
    | 0 => Fin.castAdd _ j
    | ⟨i + 1, h⟩ => Fin.natAdd _ (embedSum ⟨i, Nat.succ_lt_succ_iff.mp h⟩ j))

∃ S : Finset ι,
          S.card ≥ (1 - δ) * (Fintype.card ι) ∧
        ∃ u : (ι → F),
          u ∈ (code φ degree) ∧ ∀ i : Fin m, ∀ x ∈ S, f i x = u x

lemma degree_W (i : Fin r) : (W 𝔽q β i).degree = (Fintype.card 𝔽q)^i.val

omit [Fintype F] in
private lemma d_eq_sum {B : Finset (Fin n → F)}
  (h_B : 2 ≤ B.card)
  :
  2 * choose_2 B.card * d B =
  ∑ i, ∑ x ∈ B ×ˢ B with x.1 ≠ x.2, (if x.1 i ≠ x.2 i then 1 else 0)

@[simp]
lemma eval_solutionToQ {x : F} :
  eval x (solutionToQ e k v) =
  ∑ i ∈ Finset.range (e + k), liftF v (e + i) * x ^ i

private lemma comp_x_square_coeff_pos_deg {f : Polynomial F} {n : ℕ} (h : 0 < f.degree) :
  (f.comp (X * X)).coeff n = if Even n then f.coeff (n / 2) else 0

theorem rightpad_getElem_eq_getD {a b : List α} {unit : α} {i : Nat}
  (h : i < (a.rightpad b.length unit).length) :
    (a.rightpad b.length unit)[i] = a.getD i unit

@[simp, grind _=_]
lemma degreeY_mul [IsDomain F] (f g : F[X][Y]) (hf : f ≠ 0) (hg : g ≠ 0)
  : natDegreeY (f * g) = natDegreeY f + natDegreeY g

@[simp] theorem rightpad_length (n : Nat) (unit : α) (l : List α) :
    (rightpad n unit l).length = max n l.length

theorem liftContext_runToRound
    {lens : Context.Lens OuterStmtIn OuterStmtOut InnerStmtIn InnerStmtOut
                        OuterWitIn OuterWitOut InnerWitIn InnerWitOut}
    {outerStmtIn : OuterStmtIn} {outerWitIn : OuterWitIn} {i : Fin (n + 1)}
    (P : Prover oSpec InnerStmtIn InnerWitIn InnerStmtOut InnerWitOut pSpec) :
      (P.liftContext lens).runToRound i outerStmtIn outerWitIn
      = do
        let ⟨transcript, prvState⟩ ←
          (P.runToRound i).uncurry (lens.proj (outerStmtIn, outerWitIn))
        return ⟨transcript, ⟨prvState, outerStmtIn, outerWitIn⟩⟩

@[simp] theorem equiv_symm {p q : UniPoly Q} : equiv p q → equiv q p

omit h_β₀_eq_1 in
theorem sDomainFin_bijective (i : Fin r) (h_i : i < ℓ + R_rate)
: Function.Bijective
  (sDomainFinEquiv 𝔽q β h_ℓ_add_R_rate i h_i)

lemma concrete_mul_inv_cancel
  (prevBTFieldResult : ConcreteBTFStepResult (k := k - 1))
  (a : ConcreteBTField k) (h : a ≠ 0) :
  concrete_mul a (concrete_inv a) = one

omit [DecidableEq F] in
@[simp]
lemma isBerlekampWelchSolution_zero_zero [NeZero n] {v : Fin (2 * 0 + 0) → F} :
  IsBerlekampWelchSolution 0 0 ωs f v ↔ f = 0

@[simp]
lemma erase_even_empty :
    erase_even ∅ = ∅

lemma definingPoly_coeffOf0 {F : Type*} [Field F] [Fintype F] (s : F) [NeZero s] :
    (definingPoly s).coeff 0 = 1

theorem append_rbrKnowledgeSoundness (V₁ : OracleVerifier oSpec Stmt₁ OStmt₁ Stmt₂ OStmt₂ pSpec₁)
    (V₂ : OracleVerifier oSpec Stmt₂ OStmt₂ Stmt₃ OStmt₃ pSpec₂)
    {rbrKnowledgeError₁ : pSpec₁.ChallengeIdx → ℝ≥0}
    {rbrKnowledgeError₂ : pSpec₂.ChallengeIdx → ℝ≥0}
    (h₁ : V₁.rbrKnowledgeSoundness init impl rel₁ rel₂ rbrKnowledgeError₁)
    (h₂ : V₂.rbrKnowledgeSoundness init impl rel₂ rel₃ rbrKnowledgeError₂) :
      (V₁.append V₂).rbrKnowledgeSoundness init impl rel₁ rel₃
        (Sum.elim rbrKnowledgeError₁ rbrKnowledgeError₂ ∘ ChallengeIdx.sumEquiv.symm)

Nat.mul_le_mul_right in Init.Data.Nat.Basic

@[simp]
theorem insertNth_last : insertNth (Fin.last n) y s = snoc s y

theorem drop_repeat {α : Type*} {n' : ℕ} (m : ℕ) (h : m ≤ n) (a : Fin n' → α) :
    drop (m * n') (Nat.mul_le_mul_right n' h) (Fin.repeat n a) =
      fun i : Fin (n * n' - m * n') =>
          (Fin.repeat (n - m) a (i.cast (Nat.sub_mul n m n').symm))

lemma BerlekampWelch_E_ne_zero {e k : ℕ}
  {ωs f : Fin n → F}
  {E Q : Polynomial F}
  (h_cond : BerlekampWelchCondition e k ωs f E Q)
  : E ≠ 0

@[simp]
lemma two_mul_inv_two : (2 : F) * 2⁻¹ = 1

@[simp]
theorem removeNth_apply : removeNth p s i = s (p.succAbove i)

@[simp]
theorem eqPolynomial_eval_zeroOne (r x : σ → Fin 2) :
    eval (x : σ → R) (eqPolynomial r) = if x = r then 1 else 0

lemma schwartz_zippel_of_fintype {p : MvPolynomial σ R} (hp : p ≠ 0) (S : σ → Finset R) :
    #{x ∈ S ^^ σ | eval x p = 0} / ∏ i, (#(S i) : ℚ≥0) ≤ ∑ i, (p.degreeOf i / #(S i) : ℚ≥0)

theorem induction_init {n : ℕ} {motive : Fin (n + 2) → Sort*} {zero : motive 0}
    {succ : ∀ i : Fin (n + 1), motive i.castSucc → motive i.succ} {i : Fin (n + 1)} :
      induction (motive := motive) zero succ i.castSucc =
        induction (motive := Fin.init motive) zero (fun j x => succ j.castSucc x) i

theorem split_mul_eq_mul_split {k : ℕ} (h_pos : k > 0) (x₀ x₁ : ConcreteBTField k)
  (hi₀ lo₀ hi₁ lo₁ : ConcreteBTField (k - 1))
  (h_split_x₀ : split h_pos x₀ = (hi₀, lo₀))
  (h_split_x₁ : split h_pos x₁ = (hi₁, lo₁)) :
  split h_pos (x₀ * x₁) =
    (lo₀ * hi₁ + lo₁ * hi₀ + hi₀ * hi₁ * Z (k - 1), lo₀ * lo₁ + hi₀ * hi₁)

theorem mem_restrictDegree_iff_degreeOf_le (p : MvPolynomial σ R) (n : ℕ) :
    p ∈ restrictDegree σ R n ↔ ∀ i, p.degreeOf i ≤ n

theorem eval_comp_eval_C_finSuccEquiv (p : R[X (Fin (n + 1))]) (y : Fin n → R) (x : R) :
    eval y (Polynomial.eval (C x) (finSuccEquiv R n p)) = eval (Fin.cons x y) p

theorem dfoldl_congr_dcast {n : ℕ}
    {ι : Type v} {α α' : Fin (n + 1) → ι} {β : ι → Type u} [DCast ι β]
    {f : (i : Fin n) → β (α i.castSucc) → β (α i.succ)}
    {f' : (i : Fin n) → β (α' i.castSucc) → β (α' i.succ)}
    {init : β (α 0)} {init' : β (α' 0)}
    (hα : ∀ i, α i = α' i)
    (hf : ∀ i a, f i a = (dcast (hα _).symm (f' i (dcast (hα _) a))))
    (hinit : init = dcast (hα 0).symm init') :
      dfoldl n (fun i => β (α i)) f init =
        cast (by have := funext hα; subst this; simp) (dfoldl n (fun i => β (α' i)) f' init')

lemma add_eq_one_iff (a b : ConcreteBTField 0) :
  a + b = 1 ↔ (a = 0 ∧ b = 1) ∨ (a = 1 ∧ b = 0)

lemma getLowBits_succ {n: ℕ} (numLowBits: ℕ) :
    getLowBits (numLowBits + 1) n = getLowBits numLowBits n
    + (getBit numLowBits n) <<< numLowBits

theorem is_prime : Nat.Prime fieldSize

Fin.coe_castSucc in Init.Data.Fin.Lemmas

lemma liftF'_liftF_of_lt {k : Fin m} (h : k < n) :
  liftF' (n := m) (liftF (n := n) f') k = f' ⟨k, by omega⟩

theorem eq_zero_or_eq_one {a : ConcreteBTField 0} : a = zero ∨ a = one

@[local grind _=_]
private lemma support_eq_support_toFinsupp {f : F[X][Y]} : f.support = f.toFinsupp.support

lemma evenize_eval {f : Polynomial F} {s : F} :
    (evenize f).eval s = f.eval (s * s)

theorem findIdxRev?_eq_none {cond} {as : Array α} (h : ∀ i, (hi : i < as.size) → ¬ cond as[i]) :
  findIdxRev? cond as = none

theorem canonical_empty : (UniPoly.mk (R:=R) #[]).trim = #[]

@[to_additive (attr := simp)]
theorem prod_insertNth [CommMonoid β] {n : ℕ} (x : β) (f : Fin n → β) (p : Fin (n + 1)) :
    ∏ i, insertNth p x f i = x * ∏ i, f i

@[simp]
theorem vflatten_zero {n : Fin 0 → ℕ} {v : (i : Fin 0) → Fin (n i) → α} : vflatten v = !v[]
</all_available_lemmas>

<local_ctx>
import ArkLib.Data.Classes.DCast

import ArkLib.Data.FieldTheory.BinaryField.Tower.Basic

namespace ConcreteBinaryTower

open Polynomial

def ConcreteBTField : ℕ → Type := fun k => BitVec (2 ^ k)

section BitVecDCast

instance BitVec.instDCast : DCast Nat BitVec where
  dcast h := BitVec.cast h
  dcast_id := by admit /- proof elided -/

end BitVecDCast

section ConversionUtils

instance ConcreteBTField.instDCast_local : DCast ℕ ConcreteBTField where
  dcast h_k_eq term_k1 := BitVec.cast (congrArg (fun n => 2 ^ n) h_k_eq) term_k1
  dcast_id := by admit /- proof elided -/

end ConversionUtils

section NumericLemmas

end NumericLemmas

section FieldOperationsAndInstances

def zero {k : ℕ} : ConcreteBTField k := BitVec.zero (2 ^ k)

def one {k : ℕ} : ConcreteBTField k := 1#(2 ^ k)

def split {k : ℕ} (h : k > 0) (x : ConcreteBTField k) :
    ConcreteBTField (k - 1) × ConcreteBTField (k - 1) :=
  let lo_bits : BitVec (2 ^ (k - 1) - 1 - 0 + 1) :=
    BitVec.extractLsb (hi := 2 ^ (k - 1) - 1) (lo := 0) x
  let hi_bits : BitVec (2 ^ k - 1 - 2 ^ (k - 1) + 1) :=
    BitVec.extractLsb (hi := 2 ^ k - 1) (lo := 2 ^ (k - 1)) x
  have h_lo : 2 ^ (k - 1) - 1 - 0 + 1 = 2 ^ (k - 1) := by admit /- proof elided -/

def join {k : ℕ} (h_pos : k > 0) (hi lo : ConcreteBTField (k - 1)) : ConcreteBTField k :=

def Z (k : ℕ) : ConcreteBTField k :=
  if h_k : k = 0 then one
  else
    《 one (k:=k-1), zero (k:=k-1) 》

def concrete_mul {k : ℕ} (a b : ConcreteBTField k) : ConcreteBTField k :=
  if h_k_zero : k = 0 then
    if a = zero then zero
    else if b = zero then zero
    else if a = one then b
    else if b = one then a
    else zero 
  else
    have h_k_gt_0 : k > 0 := by admit /- proof elided -/

section FieldLemmasOfLevel0
</local_ctx>

<target_theorem>
lemma concrete_mul_left_distrib0 (a b c : ConcreteBTField 0) :
  concrete_mul a (b + c) = concrete_mul a b + concrete_mul a c :=
</target_theorem>

