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>
Bool in Init.Prelude
Nat in Init.Prelude
BitVec in Init.Prelude
BitVec.adcb in Init.Data.BitVec.Bitblast
Prod in Init.Prelude
Fin in Init.Prelude
BitVec.iunfoldr in Init.Data.BitVec.Folds
FinEnum in Mathlib.Data.FinEnum
FinEnum.card in Mathlib.Data.FinEnum
Polynomial.X in Mathlib.Algebra.Polynomial.Basic
ZMod in Mathlib.Data.ZMod.Defs
BEq in Init.Prelude
DecidableEq in Init.Prelude
Hashable in Init.Prelude
Repr in Init.Data.Repr
Std.HashMap in Std.Data.HashMap.Basic
Std.HashSet in Std.Data.HashSet.Basic
Array in Init.Prelude
List.map in Init.Prelude
Array.foldl in Init.Data.Array.Basic
Std.HashMap.emptyWithCapacity in Std.Data.HashMap.Basic
Array.size in Init.Prelude
List in Init.Prelude
Vector in Init.Data.Vector.Basic
String in Init.Prelude
Unit in Init.Prelude
Field in Mathlib.Algebra.Field.Defs
FinEnum.equiv in Mathlib.Data.FinEnum
NFA in Mathlib.Computability.NFA
NFA.accept in Mathlib.Computability.NFA
NFA.start in Mathlib.Computability.NFA
NFA.step in Mathlib.Computability.NFA
FinEnum.toList in Mathlib.Data.FinEnum
BitVec.ofNat in Init.Prelude
BitVec.cons in Init.Data.BitVec.Basic
BitVec.cast in Init.Data.BitVec.Basic
Function.Injective in Init.Data.Function
Function.LeftInverse in Init.Data.Function
</used_lib_defs>

<used_repo_defs>
def carry (initCarry : Bool) (x y : BitStream) : BitStream :=
  fun n => (addAux' initCarry x y n).2

def BitStream : Type := Nat → Bool

def addAux' (carryIn : Bool) (x y : BitStream) (i : Nat) :  Bool × Bool :=
  let carryIn : Bool := match i with
    | 0 => carryIn
    | i + 1 => (addAux' carryIn x y i).2
  Prod.swap (BitVec.adcb (x i) (y i) carryIn)

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

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

def worklistRun (final : S → Bool) (inits : Array S)
    (hinits : inits.toList.Nodup) (f : S → Array (BitVec n × S)) : CNFA n :=
  ⟨worklistRun' _ S final inits hinits f, worklistRun'_wf (BitVec n) S⟩

def worklistRun' (final : S → Bool) (inits : Array S) (hinits : inits.toList.Nodup) (f : S → Array (A × S)) : RawCNFA A :=
  let st0 := worklist.initState _ _ inits hinits final
  go st0
where go (st0 : worklist.St A S) : RawCNFA A :=
  if hemp : st0.worklist.isEmpty then st0.m else
  let sa? := st0.worklist.back?
  match heq : sa? with
  | some sa =>
    let wl := st0.worklist.pop
    let st1 := { st0 with worklist := wl,
                          worklist_nodup := by admit /- proof elided -/

structure worklist.St where
  m : RawCNFA A
  map : Std.HashMap S State := ∅
  worklist : Array S := ∅
  worklist_nodup : worklist.toList.Nodup
  worklist_incl : ∀ sa ∈ worklist, sa ∈ map

def worklist.initState (inits : Array S) (hinits : inits.toList.Nodup) (final? : S → Bool) : worklist.St A S :=
  let m := RawCNFA.empty (A := A)
  let mapm := inits.foldl (init := (Std.HashMap.emptyWithCapacity, m)) fun (map, m) sa =>
    let (s, m) := m.newState
    let m := m.addInitial s
    let m := if final? sa then m.addFinal s else m
    (map.insert sa s, m)
  let map := mapm.1
  let m := mapm.2
  let worklist_incl : ∀ sa ∈ inits, sa ∈ map :=

instance RawCNFA.statesFinset (m : RawCNFA A) : Fintype m.states := (Finset.range m.stateMax).fintypeCoeSort

abbrev State := Nat

def RawCNFA.empty : RawCNFA A := {
  stateMax := 0
  initials := ∅
  finals := ∅
  trans := ∅
}

def processOneElem (final : S → Bool) (s : State) (st : worklist.St A S) : A × S → worklist.St A S :=
  fun (a', sa') =>
    let (s', st') := st.addOrCreateState _ _ (final sa') sa'
    let m := st'.m.addTrans a' s s'
    { st' with m }

def worklist.St.addOrCreateState (st : worklist.St A S) (final? : Bool) (sa : S) : State × worklist.St A S :=
  match heq : st.map[sa]? with
  | some s => (s, st)
  | none =>
    let (s, m) := st.m.newState
    let m := if final? then m.addFinal s else m
    let map := st.map.insert sa s
    let worklist := st.worklist.push sa
    have worklist_nodup : worklist.toList.Nodup := by admit /- proof elided -/

structure CNFA (n : Nat) where
  m : RawCNFA (BitVec n)
  wf : m.WF

structure FSM (arity : Type) : Type 1 where
   
  ( α  : Type )
  [ i : FinEnum α ]
  [ h : Hashable α ]
  [ dec_eq : DecidableEq α ]
   
  ( initCarry : α → Bool )
   
  outputCirc : Circuit (α ⊕ arity)
  nextStateCirc : α → Circuit (α ⊕ arity)

inductive Circuit (α : Type u) : Type u
  | tru : Circuit α
  | fals : Circuit α
   
  | var : (positive: Bool) → α → Circuit α
  | and : Circuit α → Circuit α → Circuit α
  | or : Circuit α → Circuit α → Circuit α
  | xor : Circuit α → Circuit α → Circuit α
deriving Repr, DecidableEq

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

def bv2 : BitVec 4 := BitVec.ofNat 4 1 

def bv1 : BitVec 4 := BitVec.ofNat 4 5 
</used_repo_defs>

<lib_lemmas>
List.nodup_singleton in Mathlib.Data.List.Nodup
BitVec.eq_of_getLsbD_eq in Init.Data.BitVec.Bootstrap
BitVec.getLsbD_append in Init.Data.BitVec.Lemmas
BitVec.ofBool_eq_iff_eq in Init.Data.BitVec.Lemmas
Function.LeftInverse.injective in Init.Data.Function
BitVec.cons_msb_setWidth in Init.Data.BitVec.Bootstrap
BitVec.setWidth_cons in Init.Data.BitVec.Lemmas
List.foldl_cons in Init.Data.List.Basic
and_self in Init.SimpLemmas
and_true in Init.SimpLemmas
or_true in Init.SimpLemmas
</lib_lemmas>

<repo_lemmas>
@[ext]
theorem ext {x y : BitStream} (h : ∀ i, x i = y i) : x = y
</repo_lemmas>

<local_ctx>
import Batteries.Data.Fin.Basic

import Batteries.Data.Fin.Lemmas

import Blase.SingleWidth.Defs

import Blase.AutoStructs.Constructions

import Blase.AutoStructs.Defs

import Blase.AutoStructs.FiniteStateMachine

import Mathlib.Tactic.Ring

import Mathlib.Data.Nat.Size -- TODO: remove and get rid of shiftLeft_eq_mul_pow use

import Mathlib.Data.BitVec

import Mathlib.Tactic.FinCases

open Fin.NatCast

open Mathlib

section fsm

abbrev Alphabet (arity: Type) [FinEnum arity] := BitVec (FinEnum.card arity + 1)

variable {arity : Type} [FinEnum arity]

def finFunToBitVec [fe : FinEnum carry] (c : carry → Bool) : BitVec (FinEnum.card carry) :=
  BitVec.ofFn fun i => c (fe.equiv.invFun i)

def bitVecToFinFun [FinEnum ar] (bv : BitVec $ FinEnum.card ar) : ar → Bool :=
  fun c => bv[FinEnum.equiv.toFun c]

def NFA.ofFSM (p : FSM arity) : NFA (Alphabet arity) (p.α → Bool) where
  start := { q | q = p.initCarry }
  accept := ⊤
  step s a := {s' |
    let (s'', b) := p.nextBit s (bitVecToFinFun (a.truncate $ FinEnum.card arity))
    s' = s'' ∧ a.msb = b }

open BitStream in

def CNFA.ofFSM (p : FSM arity) : CNFA (FinEnum.card arity + 1) :=
  worklistRun (BitVec (FinEnum.card p.α))
    (fun _ => true)
    #[finFunToBitVec p.initCarry]
    (by admit /- proof elided -/
    )
    f
  where
</local_ctx>

<target_theorem>
@[simp]
lemma CNFA.ofFSM.f_spec {p : FSM arity} {s s' : BitVec (FinEnum.card p.α)} :
    (a, s') ∈ f p s ↔ bitVecToFinFun s' ∈ (NFA.ofFSM p).step (bitVecToFinFun s) a :=
</target_theorem>

