import Mathlib
import OAI.Computability.MaxCut.Machines.CompareLoop
import OAI.Computability.MaxCut.Machines.MachineCloudPrefix
import OAI.Computability.MaxCut.PCP.ExpanderRowControl

namespace OAI

namespace MaxCutGames.Foundations.Complexity.MachineFixedDivMod

open Turing
open Reduction.MachineSubstitution (pushWord stepAux_pushWord statementPushBound_pushWord)

variable {K Λ σ : Type} [DecidableEq K]

abbrev Alphabet (_ : K) := Bool
abbrev State (σ : Type) (d : Nat) := (σ × Fin d) × Option Bool

def residue (d : Nat) (positive : 0 < d) (n : Nat) : Fin d :=
  ⟨n % d, Nat.mod_lt n positive⟩

def nextResidue (d : Nat) (positive : 0 < d) (r : Fin d) : Fin d :=
  residue d positive (r.val + 1)

theorem nextResidue_residue (d : Nat) (positive : 0 < d) (n : Nat) :
    nextResidue d positive (residue d positive n) = residue d positive (n + 1) := by
  apply Fin.ext
  change (n % d + 1) % d = (n + 1) % d
  simp only [Nat.add_mod, Nat.mod_mod]

def scanLoop (d : Nat) (positive : 0 < d) (source quotient : K)
    (scanLabel : Λ) (emitterLabel : Fin d → Λ) :
    TM2.Stmt (Alphabet (K := K)) Λ (State σ d) :=
  .pop source (fun state head => (state.1, head))
    (.branch (fun state => state.2.getD false)
      (.branch (fun state => decide ((nextResidue d positive state.1.2).val = 0))
        (.push quotient (fun _ => true)
          (.load (fun state => ((state.1.1, nextResidue d positive state.1.2), state.2))
            (.goto fun _ => scanLabel)))
        (.load (fun state => ((state.1.1, nextResidue d positive state.1.2), state.2))
          (.goto fun _ => scanLabel)))
      (.push source (fun _ => false) (.goto fun state => emitterLabel state.1.2)))

/-- Each emitter is a fixed finite statement indexed by one of the `d` residues. -/
def emitter (d : Nat) (positive : 0 < d) (remainder : K) (exit : Option Λ)
    (r : Fin d) : TM2.Stmt (Alphabet (K := K)) Λ (State σ d) :=
  pushWord remainder (List.replicate r.val true)
    (.load (fun state => ((state.1.1, residue d positive 0), none))
      (Reduction.MachineTransfer.exitAt remainder exit))

omit [DecidableEq K] in
theorem scanPushBound (d : Nat) (positive : 0 < d) (source quotient : K)
    (scanLabel : Λ) (emitterLabel : Fin d → Λ) :
    Runtime.statementPushBound (scanLoop (σ := σ) d positive source quotient scanLabel
      emitterLabel) = 1 := rfl

omit [DecidableEq K] in
theorem emitterPushBound (d : Nat) (positive : 0 < d) (remainder : K)
    (exit : Option Λ) (r : Fin d) :
    Runtime.statementPushBound (emitter (σ := σ) d positive remainder exit r) = r.val := by
  cases exit <;>
    simp [emitter, statementPushBound_pushWord, Runtime.statementPushBound,
      Reduction.MachineTransfer.exitAt]

/-- Three designated tapes, with the complete surrounding tape family retained. -/
abbrev tapes (source quotient remainder : K) (base : K → List Bool)
    (input quotientWord remainderWord : List Bool) : K → List Bool :=
  MachineCopy.forkTapes source quotient remainder base input quotientWord remainderWord

def unaryTapes (source quotient remainder : K) (base : K → List Bool)
    (n q r : Nat) (sourceSuffix quotientSuffix remainderSuffix : List Bool) : K → List Bool :=
  tapes source quotient remainder base (encodeWord n ++ sourceSuffix)
    (encodeWord q ++ quotientSuffix) (encodeWord r ++ remainderSuffix)

@[simp] theorem unaryTapes_source (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (base : K → List Bool) (n q r : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) :
    unaryTapes source quotient remainder base n q r sourceSuffix quotientSuffix
      remainderSuffix source = encodeWord n ++ sourceSuffix := by
  simp [unaryTapes, sourceQuotient, sourceRemainder]

@[simp] theorem unaryTapes_quotient (source quotient remainder : K)
    (quotientRemainder : quotient ≠ remainder) (base : K → List Bool) (n q r : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) :
    unaryTapes source quotient remainder base n q r sourceSuffix quotientSuffix
      remainderSuffix quotient = encodeWord q ++ quotientSuffix := by
  simp [unaryTapes, quotientRemainder]

@[simp] theorem unaryTapes_remainder (source quotient remainder : K)
    (base : K → List Bool) (n q r : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) :
    unaryTapes source quotient remainder base n q r sourceSuffix quotientSuffix
      remainderSuffix remainder = encodeWord r ++ remainderSuffix := by
  simp [unaryTapes]

theorem unaryTapes_other (source quotient remainder other : K)
    (notSource : other ≠ source) (notQuotient : other ≠ quotient)
    (notRemainder : other ≠ remainder) (base : K → List Bool) (n q r : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) :
    unaryTapes source quotient remainder base n q r sourceSuffix quotientSuffix
      remainderSuffix other = base other := by
  simp [unaryTapes, tapes, MachineCopy.forkTapes, notSource, notQuotient, notRemainder]

private theorem update_source_inline_MachineFixedDivMod (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (base : K → List Bool)
    (input quotientWord remainderWord replacement : List Bool) :
    Function.update (tapes source quotient remainder base input quotientWord remainderWord)
      source replacement = tapes source quotient remainder base replacement quotientWord remainderWord := by
  funext k
  by_cases hs : k = source
  · subst k
    simp [tapes, MachineCopy.forkTapes, sourceQuotient, sourceRemainder]
  · by_cases hq : k = quotient
    · subst k
      simp [tapes, MachineCopy.forkTapes, Ne.symm sourceQuotient, quotientRemainder]
    · by_cases hr : k = remainder
      · subst k
        simp [tapes, MachineCopy.forkTapes, Ne.symm sourceRemainder]
      · simp [tapes, MachineCopy.forkTapes, hs, hq, hr]

private theorem update_quotient_inline_MachineFixedDivMod (source quotient remainder : K)
    (quotientRemainder : quotient ≠ remainder) (base : K → List Bool)
    (input quotientWord remainderWord replacement : List Bool) :
    Function.update (tapes source quotient remainder base input quotientWord remainderWord)
      quotient replacement = tapes source quotient remainder base input replacement remainderWord := by
  funext k
  by_cases hq : k = quotient
  · subst k
    simp [tapes, MachineCopy.forkTapes, quotientRemainder]
  · by_cases hr : k = remainder
    · subst k
      simp [tapes, MachineCopy.forkTapes, Ne.symm quotientRemainder]
    · simp [tapes, MachineCopy.forkTapes, hq, hr]

private theorem update_remainder_inline_MachineFixedDivMod (source quotient remainder : K) (base : K → List Bool)
    (input quotientWord remainderWord replacement : List Bool) :
    Function.update (tapes source quotient remainder base input quotientWord remainderWord)
      remainder replacement = tapes source quotient remainder base input quotientWord replacement := by
  simp [tapes, MachineCopy.forkTapes]

theorem scanAux_true (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (base : K → List Bool) (input quotientWord remainderWord : List Bool)
    (ambient : σ) (r : Fin d) (register : Option Bool) :
    TM2.stepAux (scanLoop d positive source quotient scanLabel emitterLabel)
      ((ambient, r), register)
      (tapes source quotient remainder base (true :: input) quotientWord remainderWord) =
      ⟨some scanLabel, ((ambient, nextResidue d positive r), some true),
        tapes source quotient remainder base input
          (if (nextResidue d positive r).val = 0 then true :: quotientWord else quotientWord)
          remainderWord⟩ := by
  by_cases hcarry : (nextResidue d positive r).val = 0 <;>
    simp [scanLoop, TM2.stepAux, sourceQuotient, sourceRemainder, quotientRemainder,
      update_source_inline_MachineFixedDivMod, update_quotient_inline_MachineFixedDivMod, hcarry]

theorem scanAux_false (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (base : K → List Bool) (input quotientWord remainderWord : List Bool)
    (ambient : σ) (r : Fin d) (register : Option Bool) :
    TM2.stepAux (scanLoop d positive source quotient scanLabel emitterLabel)
      ((ambient, r), register)
      (tapes source quotient remainder base (false :: input) quotientWord remainderWord) =
      ⟨some (emitterLabel r), ((ambient, r), some false),
        tapes source quotient remainder base (false :: input) quotientWord remainderWord⟩ := by
  simp [scanLoop, TM2.stepAux, sourceQuotient, sourceRemainder, quotientRemainder,
    update_source_inline_MachineFixedDivMod]

/-- A scan transition updates the actual quotient and finite residue of the
already-processed count. The count itself is a proof index, not machine state. -/
theorem scanStep_succ (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (base : K → List Bool) (n k : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (register : Option Bool) :
    TM2.step program ⟨some scanLabel, ((ambient, residue d positive k), register),
      unaryTapes source quotient remainder base (n + 1) (k / d) 0
        sourceSuffix quotientSuffix remainderSuffix⟩ =
      some ⟨some scanLabel, ((ambient, residue d positive (k + 1)), some true),
        unaryTapes source quotient remainder base n ((k + 1) / d) 0
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  change some (TM2.stepAux (program scanLabel) ((ambient, residue d positive k), register)
    (unaryTapes source quotient remainder base (n + 1) (k / d) 0
      sourceSuffix quotientSuffix remainderSuffix)) = _
  rw [atScan]
  simp only [unaryTapes, encodeWord, List.replicate_succ, List.cons_append]
  rw [scanAux_true d positive source quotient remainder sourceQuotient sourceRemainder
    quotientRemainder, nextResidue_residue]
  by_cases hmod : (k + 1) % d = 0
  · rw [Nat.succ_div_of_mod_eq_zero hmod]
    simp [residue, hmod, List.replicate_succ]
  · rw [Nat.succ_div_of_mod_ne_zero hmod]
    simp [residue, hmod]

theorem scanStep_zero (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (base : K → List Bool) (q : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (r : Fin d) (register : Option Bool) :
    TM2.step program ⟨some scanLabel, ((ambient, r), register),
      unaryTapes source quotient remainder base 0 q 0
        sourceSuffix quotientSuffix remainderSuffix⟩ =
      some ⟨some (emitterLabel r), ((ambient, r), some false),
        unaryTapes source quotient remainder base 0 q 0
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  change some (TM2.stepAux (program scanLabel) ((ambient, r), register)
    (unaryTapes source quotient remainder base 0 q 0
      sourceSuffix quotientSuffix remainderSuffix)) = _
  rw [atScan]
  simp only [unaryTapes, encodeWord, List.replicate_zero, List.nil_append,
    List.singleton_append]
  rw [scanAux_false d positive source quotient remainder sourceQuotient sourceRemainder
    quotientRemainder]

theorem emitterStep (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (emitterLabel : Fin d → Λ) (exit : Option Λ)
    (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atEmitter : ∀ r, program (emitterLabel r) = emitter d positive remainder exit r)
    (base : K → List Bool) (n q : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (r : Fin d) (register : Option Bool) :
    TM2.step program ⟨some (emitterLabel r), ((ambient, r), register),
      unaryTapes source quotient remainder base n q 0
        sourceSuffix quotientSuffix remainderSuffix⟩ =
      some ⟨exit, ((ambient, residue d positive 0), none),
        unaryTapes source quotient remainder base n q r.val
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  change some (TM2.stepAux (program (emitterLabel r)) ((ambient, r), register)
    (unaryTapes source quotient remainder base n q 0
      sourceSuffix quotientSuffix remainderSuffix)) = _
  rw [atEmitter]
  unfold emitter
  rw [stepAux_pushWord]
  simp only [unaryTapes, MachineCopy.forkTapes_right, List.reverse_replicate]
  rw [update_remainder_inline_MachineFixedDivMod]
  cases exit <;>
    simp [TM2.stepAux, Reduction.MachineTransfer.exitAt, encodeWord, List.append_assoc]

/-- The general invariant starts at the finite residue and unary quotient of
`k`, then scans `n` additional input bits. It is an actual execution theorem. -/
theorem trace_fromCount (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (exit : Option Λ) (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (atEmitter : ∀ r, program (emitterLabel r) = emitter d positive remainder exit r)
    (base : K → List Bool) (n k : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (register : Option Bool) :
    (MachineComposition.advance (TM2.step program))^[n + 2]
      (some ⟨some scanLabel, ((ambient, residue d positive k), register),
        unaryTapes source quotient remainder base n (k / d) 0
          sourceSuffix quotientSuffix remainderSuffix⟩) =
      some ⟨exit, ((ambient, residue d positive 0), none),
        unaryTapes source quotient remainder base 0 ((k + n) / d) ((k + n) % d)
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  induction n generalizing k register with
  | zero =>
    change (TM2.step program ⟨some scanLabel, ((ambient, residue d positive k), register),
      unaryTapes source quotient remainder base 0 (k / d) 0
        sourceSuffix quotientSuffix remainderSuffix⟩).bind (TM2.step program) = _
    rw [scanStep_zero d positive source quotient remainder sourceQuotient sourceRemainder
      quotientRemainder scanLabel emitterLabel program atScan, Option.bind_some]
    simpa only [residue, Nat.add_zero] using
      emitterStep d positive source quotient remainder emitterLabel exit program atEmitter
        base 0 (k / d) sourceSuffix quotientSuffix remainderSuffix ambient
        (residue d positive k) (some false)
  | succ n ih =>
    rw [Function.iterate_succ_apply]
    change (MachineComposition.advance (TM2.step program))^[n + 2]
      (TM2.step program ⟨some scanLabel, ((ambient, residue d positive k), register),
        unaryTapes source quotient remainder base (n + 1) (k / d) 0
          sourceSuffix quotientSuffix remainderSuffix⟩) = _
    rw [scanStep_succ d positive source quotient remainder sourceQuotient sourceRemainder
      quotientRemainder scanLabel emitterLabel program atScan]
    simpa only [Nat.add_assoc, Nat.add_comm, Nat.add_left_comm] using ih (k + 1) (some true)

/-- Exact unary quotient and remainder, with both output counters initially zero. -/
theorem divModTrace (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (exit : Option Λ) (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (atEmitter : ∀ r, program (emitterLabel r) = emitter d positive remainder exit r)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (register : Option Bool) :
    (MachineComposition.advance (TM2.step program))^[n + 2]
      (some ⟨some scanLabel, ((ambient, residue d positive 0), register),
        unaryTapes source quotient remainder base n 0 0
          sourceSuffix quotientSuffix remainderSuffix⟩) =
      some ⟨exit, ((ambient, residue d positive 0), none),
        unaryTapes source quotient remainder base 0 (n / d) (n % d)
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  simpa only [Nat.zero_add, Nat.zero_div] using
    trace_fromCount d positive source quotient remainder sourceQuotient sourceRemainder
      quotientRemainder scanLabel emitterLabel exit program atScan atEmitter base n 0
      sourceSuffix quotientSuffix remainderSuffix ambient register

/-- Caller-frame form: the only initial tape hypotheses are the three unary prefixes. -/
theorem divModFromTapes (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (exit : Option Λ) (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (atEmitter : ∀ r, program (emitterLabel r) = emitter d positive remainder exit r)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base source = encodeWord n ++ sourceSuffix)
    (quotientInput : base quotient = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base remainder = encodeWord 0 ++ remainderSuffix)
    (ambient : σ) (register : Option Bool) :
    (MachineComposition.advance (TM2.step program))^[n + 2]
      (some ⟨some scanLabel, ((ambient, residue d positive 0), register), base⟩) =
      some ⟨exit, ((ambient, residue d positive 0), none),
        unaryTapes source quotient remainder base 0 (n / d) (n % d)
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  have hbase : unaryTapes source quotient remainder base n 0 0 sourceSuffix quotientSuffix
      remainderSuffix = base := by
    simp only [unaryTapes, ← sourceInput, ← quotientInput, ← remainderInput,
      MachineCopy.forkTapes_self]
  have h := divModTrace d positive source quotient remainder sourceQuotient sourceRemainder
    quotientRemainder scanLabel emitterLabel exit program atScan atEmitter base n
    sourceSuffix quotientSuffix remainderSuffix ambient register
  rw [hbase] at h
  exact h

def divModInTime (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (exit : Option Λ) (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (atEmitter : ∀ r, program (emitterLabel r) = emitter d positive remainder exit r)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base source = encodeWord n ++ sourceSuffix)
    (quotientInput : base quotient = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base remainder = encodeWord 0 ++ remainderSuffix)
    (ambient : σ) (register : Option Bool) :
    StateTransition.EvalsToInTime (TM2.step program)
      ⟨some scanLabel, ((ambient, residue d positive 0), register), base⟩
      (some ⟨exit, ((ambient, residue d positive 0), none),
        unaryTapes source quotient remainder base 0 (n / d) (n % d)
          sourceSuffix quotientSuffix remainderSuffix⟩) (n + 2) where
  steps := n + 2
  evals_in_steps := divModFromTapes d positive source quotient remainder sourceQuotient
    sourceRemainder quotientRemainder scanLabel emitterLabel exit program atScan atEmitter
    base n sourceSuffix quotientSuffix remainderSuffix sourceInput quotientInput remainderInput
    ambient register
  steps_le_m := Nat.le_refl _

/-- Stop just before emission, retaining the final finite residue as actual control. -/
theorem scanTrace_fromCount (d : Nat) (positive : 0 < d) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (base : K → List Bool) (n k : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (register : Option Bool) :
    (MachineComposition.advance (TM2.step program))^[n + 1]
      (some ⟨some scanLabel, ((ambient, residue d positive k), register),
        unaryTapes source quotient remainder base n (k / d) 0
          sourceSuffix quotientSuffix remainderSuffix⟩) =
      some ⟨some (emitterLabel (residue d positive (k + n))),
        ((ambient, residue d positive (k + n)), some false),
        unaryTapes source quotient remainder base 0 ((k + n) / d) 0
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  induction n generalizing k register with
  | zero =>
    simpa only [Nat.zero_add, Nat.add_zero, Function.iterate_one,
      MachineComposition.advance_some] using
      scanStep_zero d positive source quotient remainder sourceQuotient sourceRemainder
        quotientRemainder scanLabel emitterLabel program atScan base (k / d)
        sourceSuffix quotientSuffix remainderSuffix ambient (residue d positive k) register
  | succ n ih =>
    rw [Function.iterate_succ_apply]
    change (MachineComposition.advance (TM2.step program))^[n + 1]
      (TM2.step program ⟨some scanLabel, ((ambient, residue d positive k), register),
        unaryTapes source quotient remainder base (n + 1) (k / d) 0
          sourceSuffix quotientSuffix remainderSuffix⟩) = _
    rw [scanStep_succ d positive source quotient remainder sourceQuotient sourceRemainder
      quotientRemainder scanLabel emitterLabel program atScan]
    simpa only [Nat.add_assoc, Nat.add_comm, Nat.add_left_comm] using ih (k + 1) (some true)

/-- A fixed table on finite ambient control may retain the residue before local reset. -/
def emitterWithFinish [Fintype σ] (d : Nat) (positive : 0 < d) (remainder : K)
    (exit : Option Λ) (finish : σ → Fin d → σ) (r : Fin d) :
    TM2.Stmt (Alphabet (K := K)) Λ (State σ d) :=
  pushWord remainder (List.replicate r.val true)
    (.load (fun state => ((finish state.1.1 r, residue d positive 0), none))
      (Reduction.MachineTransfer.exitAt remainder exit))

omit [DecidableEq K] in
theorem emitterWithFinishPushBound [Fintype σ] (d : Nat) (positive : 0 < d)
    (remainder : K) (exit : Option Λ) (finish : σ → Fin d → σ) (r : Fin d) :
    Runtime.statementPushBound (emitterWithFinish d positive remainder exit finish r) =
      r.val := by
  cases exit <;>
    simp [emitterWithFinish, statementPushBound_pushWord, Runtime.statementPushBound,
      Reduction.MachineTransfer.exitAt]

theorem emitterWithFinishStep [Fintype σ] (d : Nat) (positive : 0 < d)
    (source quotient remainder : K) (emitterLabel : Fin d → Λ) (exit : Option Λ)
    (finish : σ → Fin d → σ)
    (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atEmitter : ∀ r, program (emitterLabel r) =
      emitterWithFinish d positive remainder exit finish r)
    (base : K → List Bool) (n q : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (r : Fin d) (register : Option Bool) :
    TM2.step program ⟨some (emitterLabel r), ((ambient, r), register),
      unaryTapes source quotient remainder base n q 0
        sourceSuffix quotientSuffix remainderSuffix⟩ =
      some ⟨exit, ((finish ambient r, residue d positive 0), none),
        unaryTapes source quotient remainder base n q r.val
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  change some (TM2.stepAux (program (emitterLabel r)) ((ambient, r), register)
    (unaryTapes source quotient remainder base n q 0
      sourceSuffix quotientSuffix remainderSuffix)) = _
  rw [atEmitter]
  unfold emitterWithFinish
  rw [stepAux_pushWord]
  simp only [unaryTapes, MachineCopy.forkTapes_right, List.reverse_replicate]
  rw [update_remainder_inline_MachineFixedDivMod]
  cases exit <;>
    simp [TM2.stepAux, Reduction.MachineTransfer.exitAt, encodeWord, List.append_assoc]

/-- The callback is a fixed finite-control table, applied in the existing emitter transition. -/
theorem divModTraceWithFinish [Fintype σ] (d : Nat) (positive : 0 < d)
    (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (exit : Option Λ) (finish : σ → Fin d → σ)
    (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (atEmitter : ∀ r, program (emitterLabel r) =
      emitterWithFinish d positive remainder exit finish r)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (ambient : σ) (register : Option Bool) :
    (MachineComposition.advance (TM2.step program))^[n + 2]
      (some ⟨some scanLabel, ((ambient, residue d positive 0), register),
        unaryTapes source quotient remainder base n 0 0
          sourceSuffix quotientSuffix remainderSuffix⟩) =
      some ⟨exit, ((finish ambient (residue d positive n), residue d positive 0), none),
        unaryTapes source quotient remainder base 0 (n / d) (n % d)
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  have hscan := scanTrace_fromCount d positive source quotient remainder
    sourceQuotient sourceRemainder quotientRemainder scanLabel emitterLabel program atScan
    base n 0 sourceSuffix quotientSuffix remainderSuffix ambient register
  simp only [Nat.zero_add, Nat.zero_div] at hscan
  rw [Function.iterate_succ_apply', hscan, MachineComposition.advance_some]
  exact emitterWithFinishStep d positive source quotient remainder emitterLabel exit finish
    program atEmitter base 0 (n / d) sourceSuffix quotientSuffix remainderSuffix ambient
    (residue d positive n) (some false)

theorem divModFromTapesWithFinish [Fintype σ] (d : Nat) (positive : 0 < d)
    (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder) (scanLabel : Λ) (emitterLabel : Fin d → Λ)
    (exit : Option Λ) (finish : σ → Fin d → σ)
    (program : Λ → TM2.Stmt (Alphabet (K := K)) Λ (State σ d))
    (atScan : program scanLabel = scanLoop d positive source quotient scanLabel emitterLabel)
    (atEmitter : ∀ r, program (emitterLabel r) =
      emitterWithFinish d positive remainder exit finish r)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base source = encodeWord n ++ sourceSuffix)
    (quotientInput : base quotient = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base remainder = encodeWord 0 ++ remainderSuffix)
    (ambient : σ) (register : Option Bool) :
    (MachineComposition.advance (TM2.step program))^[n + 2]
      (some ⟨some scanLabel, ((ambient, residue d positive 0), register), base⟩) =
      some ⟨exit, ((finish ambient (residue d positive n), residue d positive 0), none),
        unaryTapes source quotient remainder base 0 (n / d) (n % d)
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  have hbase : unaryTapes source quotient remainder base n 0 0 sourceSuffix quotientSuffix
      remainderSuffix = base := by
    simp only [unaryTapes, ← sourceInput, ← quotientInput, ← remainderInput,
      MachineCopy.forkTapes_self]
  have h := divModTraceWithFinish d positive source quotient remainder sourceQuotient
    sourceRemainder quotientRemainder scanLabel emitterLabel exit finish program atScan
    atEmitter base n sourceSuffix quotientSuffix remainderSuffix ambient register
  rw [hbase] at h
  exact h

end MaxCutGames.Foundations.Complexity.MachineFixedDivMod

namespace MaxCutGames.Foundations.Complexity.MachineExpanderRow

open Turing
open PCP.ExpanderTables PCP.ExpanderRowControl

inductive Tape
  | inputVertex | table | output
  | emitScratch | queryReverse | queryIndex
  | lookupOutput | lookupWork | lookupRestore
  | quotientFirst | quotientSecond | remainderFirst | remainderSecond
  deriving DecidableEq

protected abbrev Tape.enumList : List Tape := [.inputVertex, .table, .output, .emitScratch,
  .queryReverse, .queryIndex, .lookupOutput, .lookupWork, .lookupRestore, .quotientFirst,
  .quotientSecond, .remainderFirst, .remainderSecond]

protected theorem Tape.enumList_getElem?_ctorIdx_eq (x : Tape) :
    Tape.enumList[x.ctorIdx]? = some x := by
  cases x <;> rfl

protected theorem Tape.enumList_nodup : Tape.enumList.Nodup := by decide

instance : Fintype Tape where
  elems := ⟨Tape.enumList, Tape.enumList_nodup⟩
  complete x := by cases x <;> decide

inductive Label (d : Nat)
  | initialize
  | firstEmit (label : PCP.AlphabetTable.Emitter.Label 3 (degree d))
  | firstReverse
  | firstLookup (label : MachinePreservingLookupClean.Label)
  | firstScan
  | firstResidue (r : Fin (degree d))
  | clearQuery
  | secondEmit (label : PCP.AlphabetTable.Emitter.Label 3 (degree d))
  | secondReverse
  | secondLookup (label : MachinePreservingLookupClean.Label)
  | secondScan
  | secondResidue (r : Fin (degree d))
  | outputEmit (label : PCP.AlphabetTable.Emitter.Label 3 (rowFactor d))
  | cleanup (i : Fin 6)
  | done
  deriving DecidableEq, Fintype

abbrev Ambient (ρ : Type) (d : Nat) := ρ × Control d
abbrev State (ρ : Type) (d : Nat) :=
  PCP.AlphabetTable.Emitter.State (Ambient ρ d × Fin (degree d))

/-- The residue and the emitter's unit field are just permuted; no tape is
read or written by this static change of finite state coordinates. -/
def divisionStates (ρ : Type) (d : Nat) :
    MachineFixedDivMod.State (Ambient ρ d × Unit) (degree d) ≃ State ρ d where
  toFun s := (((s.1.1.1, s.1.2), ()), s.2)
  invFun s := (((s.1.1.1, ()), s.1.1.2), s.2)
  left_inv := by rintro ⟨⟨⟨a, u⟩, r⟩, b⟩; cases u; rfl
  right_inv := by rintro ⟨⟨⟨a, r⟩, u⟩, b⟩; cases u; rfl

def firstFinish {ρ : Type} {d : Nat} (s : Ambient ρ d × Unit)
    (r : Fin (degree d)) : Ambient ρ d × Unit :=
  ((s.1.1, receiveFirst s.1.2 r), ())

def secondFinish {ρ : Type} {d : Nat} (H : Table (cloudSize d) d)
    (s : Ambient ρ d × Unit) (r : Fin (degree d)) : Ambient ρ d × Unit :=
  ((s.1.1, receiveSecond H s.1.2 r), ())

def affinePlan {σ : Type} {bound : Nat} (coefficient : Nat) (offset : σ → Fin bound) :
    Fin 3 → PCP.AlphabetTable.Emitter.Command 1 σ bound :=
  PCP.AlphabetTable.Emitter.listCommands
    (PCP.AlphabetTable.Emitter.affineCommands [(0, coefficient)] offset)

def firstPlan (ρ : Type) (d : Nat) :
    Fin 3 → PCP.AlphabetTable.Emitter.Command 1 (Ambient ρ d × Fin (degree d)) (degree d) :=
  affinePlan (degree d) (fun s => firstOffset s.1.2)

def secondPlan (ρ : Type) (d : Nat) :
    Fin 3 → PCP.AlphabetTable.Emitter.Command 1 (Ambient ρ d × Fin (degree d)) (degree d) :=
  affinePlan (degree d) (fun s => secondOffset s.1.2)

def outputPlan (ρ : Type) (d : Nat) :
    Fin 3 → PCP.AlphabetTable.Emitter.Command 1 (Ambient ρ d × Fin (degree d)) (rowFactor d) :=
  affinePlan (rowFactor d) (fun s => outputOffset s.1.2)

def lookupTape : Fin 5 → Tape
  | ⟨0, _⟩ => .table
  | ⟨1, _⟩ => .queryIndex
  | ⟨2, _⟩ => .lookupWork
  | ⟨3, _⟩ => .lookupOutput
  | _ => .lookupRestore

def dirtyTape : Fin 6 → Tape
  | ⟨0, _⟩ => .queryIndex
  | ⟨1, _⟩ => .lookupOutput
  | ⟨2, _⟩ => .quotientFirst
  | ⟨3, _⟩ => .quotientSecond
  | ⟨4, _⟩ => .remainderFirst
  | _ => .remainderSecond

variable {K Λ ρ : Type} [DecidableEq K] [Fintype ρ]

/-- Every branch is a concrete finite TM2 statement. The fixed table `H`
is evaluated only on finite control values, never on an unbounded tape value. -/
def statement {d : Nat} (positive : 0 < d) (H : Table (cloudSize d) d)
    (ports : Tape → K) (labels : Label d → Λ) (exit : Option Λ) :
    Label d → TM2.Stmt (fun _ : K => Bool) Λ (State ρ d)
  | .initialize =>
    .push (ports .quotientFirst) (fun _ => false)
      (.push (ports .quotientSecond) (fun _ => false)
        (.push (ports .remainderFirst) (fun _ => false)
          (.push (ports .remainderSecond) (fun _ => false)
            (.load (fun s => (s.1, none))
              (.goto fun _ => labels (.firstEmit (PCP.AlphabetTable.Emitter.labelAt 3 _ 0 .entry)))))))
  | .firstEmit l =>
    PCP.AlphabetTable.Emitter.statement (firstPlan ρ d) (fun _ => ports .inputVertex)
      (ports .emitScratch) (ports .queryReverse) (fun k => labels (.firstEmit k))
      (some (labels .firstReverse)) l
  | .firstReverse =>
    Reduction.MachineTransfer.loopAt (ports .queryReverse) (ports .queryIndex)
      id false (labels .firstReverse)
      (some (labels (.firstLookup (.run .copyFirst))))
  | .firstLookup l =>
    MachinePreservingLookupClean.statement (ports ∘ lookupTape)
      (fun k => labels (.firstLookup k)) (some (labels .firstScan)) l
  | .firstScan =>
    MachineControl.statement id (divisionStates ρ d)
      (MachineFixedDivMod.scanLoop (degree d) (Nat.mul_pos positive positive)
        (ports .lookupOutput) (ports .quotientFirst) (labels .firstScan)
        (fun r => labels (.firstResidue r)))
  | .firstResidue r =>
    MachineControl.statement id (divisionStates ρ d)
      (MachineFixedDivMod.emitterWithFinish (degree d) (Nat.mul_pos positive positive)
        (ports .remainderFirst) (some (labels .clearQuery)) firstFinish r)
  | .clearQuery =>
    .pop (ports .queryIndex) (fun s _ => s)
      (.pop (ports .lookupOutput) (fun s _ => s)
        (.goto fun _ => labels (.secondEmit (PCP.AlphabetTable.Emitter.labelAt 3 _ 0 .entry))))
  | .secondEmit l =>
    PCP.AlphabetTable.Emitter.statement (secondPlan ρ d) (fun _ => ports .quotientFirst)
      (ports .emitScratch) (ports .queryReverse) (fun k => labels (.secondEmit k))
      (some (labels .secondReverse)) l
  | .secondReverse =>
    Reduction.MachineTransfer.loopAt (ports .queryReverse) (ports .queryIndex)
      id false (labels .secondReverse)
      (some (labels (.secondLookup (.run .copyFirst))))
  | .secondLookup l =>
    MachinePreservingLookupClean.statement (ports ∘ lookupTape)
      (fun k => labels (.secondLookup k)) (some (labels .secondScan)) l
  | .secondScan =>
    MachineControl.statement id (divisionStates ρ d)
      (MachineFixedDivMod.scanLoop (degree d) (Nat.mul_pos positive positive)
        (ports .lookupOutput) (ports .quotientSecond) (labels .secondScan)
        (fun r => labels (.secondResidue r)))
  | .secondResidue r =>
    MachineControl.statement id (divisionStates ρ d)
      (MachineFixedDivMod.emitterWithFinish (degree d) (Nat.mul_pos positive positive)
        (ports .remainderSecond)
        (some (labels (.outputEmit (PCP.AlphabetTable.Emitter.labelAt 3 _ 0 .entry))))
        (secondFinish H) r)
  | .outputEmit l =>
    PCP.AlphabetTable.Emitter.statement (outputPlan ρ d) (fun _ => ports .quotientSecond)
      (ports .emitScratch) (ports .output) (fun k => labels (.outputEmit k))
      (some (labels (.cleanup 0))) l
  | .cleanup i =>
    MachineDrain.drain (ports (dirtyTape i)) (labels (.cleanup i))
      (some (if hi : i.val + 1 < 6 then labels (.cleanup ⟨i.val + 1, hi⟩) else labels .done))
  | .done => Reduction.MachineTransfer.exitAt (ports .output) exit

def program {d : Nat} (positive : 0 < d) (H : Table (cloudSize d) d) :
    Label d → TM2.Stmt (fun _ : Tape => Bool) (Label d) (State ρ d) :=
  statement positive H id id none

end MaxCutGames.Foundations.Complexity.MachineExpanderRow

/-!
The two actual division phases of the expander-row program. Static state
conjugation connects the fixed-divisor machine to the common emitter state.
Only the concrete statement placement equations are premises; no phase trace
or whole-row execution is assumed. Each phase has exactly `n + 2` transitions.
-/

namespace MaxCutGames.Foundations.Complexity.MachineExpanderRow

open Turing
open PCP.ExpanderTables PCP.ExpanderRowControl

private theorem controlStatement_inverse_inline_MachineExpanderRowDivision {K Λ σ τ : Type} {Γ : K → Type}
    (e : σ ≃ τ) (q : TM2.Stmt Γ Λ σ) :
    MachineControl.statement id e.symm (MachineControl.statement id e q) = q := by
  induction q <;>
    simp_all only [MachineControl.statement, Equiv.apply_symm_apply,
      Equiv.symm_apply_apply, id_eq]

/-- Pull the actual target program into division-state coordinates, derive its
trace from its concrete statements, then transport every actual transition back. -/
private theorem transportedDivision_inline_MachineExpanderRowDivision {K Λ σ τ : Type} [DecidableEq K] [Fintype σ]
    (q : Nat) (positive : 0 < q) (source quotient remainder : K)
    (sourceQuotient : source ≠ quotient) (sourceRemainder : source ≠ remainder)
    (quotientRemainder : quotient ≠ remainder)
    (states : MachineFixedDivMod.State σ q ≃ τ)
    (scanLabel : Λ) (emitterLabel : Fin q → Λ) (exit : Option Λ)
    (finish : σ → Fin q → σ)
    (target : Λ → TM2.Stmt (fun _ : K => Bool) Λ τ)
    (atScan : target scanLabel = MachineControl.statement id states
      (MachineFixedDivMod.scanLoop q positive source quotient scanLabel emitterLabel))
    (atEmitter : ∀ r, target (emitterLabel r) = MachineControl.statement id states
      (MachineFixedDivMod.emitterWithFinish q positive remainder exit finish r))
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base source = encodeWord n ++ sourceSuffix)
    (quotientInput : base quotient = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base remainder = encodeWord 0 ++ remainderSuffix)
    (ambient : σ) (register : Option Bool) :
    (MachineComposition.advance (TM2.step target))^[n + 2]
      (some (MachineControl.configuration id states
        ⟨some scanLabel, ((ambient, MachineFixedDivMod.residue q positive 0), register), base⟩)) =
      some (MachineControl.configuration id states
        ⟨exit, ((finish ambient (MachineFixedDivMod.residue q positive n),
          MachineFixedDivMod.residue q positive 0), none),
          MachineFixedDivMod.unaryTapes source quotient remainder base 0 (n / q) (n % q)
            sourceSuffix quotientSuffix remainderSuffix⟩) := by
  let sourceProgram := MachineControl.program (Equiv.refl Λ) states.symm target
  have sourceScan : sourceProgram scanLabel =
      MachineFixedDivMod.scanLoop q positive source quotient scanLabel emitterLabel := by
    change MachineControl.statement id states.symm (target scanLabel) = _
    rw [atScan]
    exact controlStatement_inverse_inline_MachineExpanderRowDivision states _
  have sourceEmit : ∀ r, sourceProgram (emitterLabel r) =
      MachineFixedDivMod.emitterWithFinish q positive remainder exit finish r := by
    intro r
    change MachineControl.statement id states.symm (target (emitterLabel r)) = _
    rw [atEmitter]
    exact controlStatement_inverse_inline_MachineExpanderRowDivision states _
  have htrace := MachineFixedDivMod.divModFromTapesWithFinish q positive source quotient
    remainder sourceQuotient sourceRemainder quotientRemainder scanLabel emitterLabel exit
    finish sourceProgram sourceScan sourceEmit base n sourceSuffix quotientSuffix remainderSuffix
    sourceInput quotientInput remainderInput ambient register
  have roundtrip : MachineControl.program (Equiv.refl Λ) states sourceProgram = target := by
    funext label
    change MachineControl.statement id states
      (MachineControl.statement id states.symm (target label)) = target label
    exact controlStatement_inverse_inline_MachineExpanderRowDivision states.symm _
  have simulation : ∀ a b, TM2.step sourceProgram a = some b →
      TM2.step target (MachineControl.configuration id states a) =
        some (MachineControl.configuration id states b) := by
    intro a b hab
    have h := MachineControl.step_simulation (Equiv.refl Λ) states sourceProgram a
    rw [roundtrip, hab] at h
    exact h
  exact MachineComposition.liftSuccessfulTrace (TM2.step sourceProgram) (TM2.step target)
    (MachineControl.configuration id states) simulation (n + 2) _ _ htrace

variable {K Λ ρ : Type} [DecidableEq K] [Fintype ρ]

@[simp] theorem divisionStates_apply (ρ : Type) (d : Nat)
    (s : MachineFixedDivMod.State (Ambient ρ d × Unit) (degree d)) :
    divisionStates ρ d s = (((s.1.1.1, s.1.2), ()), s.2) := rfl

/-- The common row state at a division boundary, with its local residue reset. -/
def divisionState {d : Nat} (positive : 0 < d) (ambient : ρ) (control : Control d)
    (register : Option Bool) : State ρ d :=
  ((((ambient, control),
    MachineFixedDivMod.residue (degree d) (Nat.mul_pos positive positive) 0), ()), register)

def divisionOutput (d : Nat) (ports : Tape → K) (quotient remainder : Tape)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) : K → List Bool :=
  MachineFixedDivMod.unaryTapes (ports .lookupOutput) (ports quotient) (ports remainder)
    base 0 (n / degree d) (n % degree d) sourceSuffix quotientSuffix remainderSuffix

/-- Exact first lookup-result division, including the receiveFirst control update. -/
theorem firstDivisionTrace {d : Nat} (positive : 0 < d) (H : Table (cloudSize d) d)
    (ports : Tape → K) (portsInjective : Function.Injective ports)
    (labels : Label d → Λ) (exit : Option Λ)
    (target : Λ → TM2.Stmt (fun _ : K => Bool) Λ (State ρ d))
    (atProgram : ∀ label, target (labels label) = statement positive H ports labels exit label)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base (ports .lookupOutput) = encodeWord n ++ sourceSuffix)
    (quotientInput : base (ports .quotientFirst) = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base (ports .remainderFirst) = encodeWord 0 ++ remainderSuffix)
    (ambient : ρ) (control : Control d) (register : Option Bool) :
    (MachineComposition.advance (TM2.step target))^[n + 2]
      (some ⟨some (labels .firstScan), divisionState positive ambient control register, base⟩) =
      some ⟨some (labels .clearQuery), divisionState positive ambient
        (receiveFirst control (MachineFixedDivMod.residue (degree d)
          (Nat.mul_pos positive positive) n)) none,
        divisionOutput d ports .quotientFirst .remainderFirst base n
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  have hsq : ports .lookupOutput ≠ ports .quotientFirst :=
    fun h => Tape.noConfusion (portsInjective h)
  have hsr : ports .lookupOutput ≠ ports .remainderFirst :=
    fun h => Tape.noConfusion (portsInjective h)
  have hqr : ports .quotientFirst ≠ ports .remainderFirst :=
    fun h => Tape.noConfusion (portsInjective h)
  have hs : target (labels .firstScan) = MachineControl.statement id (divisionStates ρ d)
      (MachineFixedDivMod.scanLoop (degree d) (Nat.mul_pos positive positive)
        (ports .lookupOutput) (ports .quotientFirst) (labels .firstScan)
        (fun r => labels (.firstResidue r))) := atProgram .firstScan
  have he : ∀ r, target (labels (.firstResidue r)) =
      MachineControl.statement id (divisionStates ρ d)
        (MachineFixedDivMod.emitterWithFinish (degree d) (Nat.mul_pos positive positive)
          (ports .remainderFirst) (some (labels .clearQuery)) firstFinish r) :=
    fun r => atProgram (.firstResidue r)
  have h := transportedDivision_inline_MachineExpanderRowDivision (degree d) (Nat.mul_pos positive positive)
    (ports .lookupOutput) (ports .quotientFirst) (ports .remainderFirst) hsq hsr hqr
    (divisionStates ρ d) (labels .firstScan) (fun r => labels (.firstResidue r))
    (some (labels .clearQuery)) firstFinish target hs he base n sourceSuffix quotientSuffix
    remainderSuffix sourceInput quotientInput remainderInput ((ambient, control), ()) register
  simpa only [MachineControl.configuration, divisionStates_apply, firstFinish, divisionState,
    divisionOutput, Option.map_some, id_eq] using h

/-- Exact second division, including receiveSecond and the actual output-emitter entry label. -/
theorem secondDivisionTrace {d : Nat} (positive : 0 < d) (H : Table (cloudSize d) d)
    (ports : Tape → K) (portsInjective : Function.Injective ports)
    (labels : Label d → Λ) (exit : Option Λ)
    (target : Λ → TM2.Stmt (fun _ : K => Bool) Λ (State ρ d))
    (atProgram : ∀ label, target (labels label) = statement positive H ports labels exit label)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base (ports .lookupOutput) = encodeWord n ++ sourceSuffix)
    (quotientInput : base (ports .quotientSecond) = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base (ports .remainderSecond) = encodeWord 0 ++ remainderSuffix)
    (ambient : ρ) (control : Control d) (register : Option Bool) :
    (MachineComposition.advance (TM2.step target))^[n + 2]
      (some ⟨some (labels .secondScan), divisionState positive ambient control register, base⟩) =
      some ⟨some (labels (.outputEmit (PCP.AlphabetTable.Emitter.labelAt 3 _ 0 .entry))),
        divisionState positive ambient
          (receiveSecond H control (MachineFixedDivMod.residue (degree d)
            (Nat.mul_pos positive positive) n)) none,
        divisionOutput d ports .quotientSecond .remainderSecond base n
          sourceSuffix quotientSuffix remainderSuffix⟩ := by
  have hsq : ports .lookupOutput ≠ ports .quotientSecond :=
    fun h => Tape.noConfusion (portsInjective h)
  have hsr : ports .lookupOutput ≠ ports .remainderSecond :=
    fun h => Tape.noConfusion (portsInjective h)
  have hqr : ports .quotientSecond ≠ ports .remainderSecond :=
    fun h => Tape.noConfusion (portsInjective h)
  have hs : target (labels .secondScan) = MachineControl.statement id (divisionStates ρ d)
      (MachineFixedDivMod.scanLoop (degree d) (Nat.mul_pos positive positive)
        (ports .lookupOutput) (ports .quotientSecond) (labels .secondScan)
        (fun r => labels (.secondResidue r))) := atProgram .secondScan
  have he : ∀ r, target (labels (.secondResidue r)) =
      MachineControl.statement id (divisionStates ρ d)
        (MachineFixedDivMod.emitterWithFinish (degree d) (Nat.mul_pos positive positive)
          (ports .remainderSecond)
          (some (labels (.outputEmit (PCP.AlphabetTable.Emitter.labelAt 3 _ 0 .entry))))
          (secondFinish H) r) := fun r => atProgram (.secondResidue r)
  have h := transportedDivision_inline_MachineExpanderRowDivision (degree d) (Nat.mul_pos positive positive)
    (ports .lookupOutput) (ports .quotientSecond) (ports .remainderSecond) hsq hsr hqr
    (divisionStates ρ d) (labels .secondScan) (fun r => labels (.secondResidue r))
    (some (labels (.outputEmit (PCP.AlphabetTable.Emitter.labelAt 3 _ 0 .entry))))
    (secondFinish H) target hs he base n sourceSuffix quotientSuffix remainderSuffix
    sourceInput quotientInput remainderInput ((ambient, control), ()) register
  simpa only [MachineControl.configuration, divisionStates_apply, secondFinish, divisionState,
    divisionOutput, Option.map_some, id_eq] using h

@[simp] theorem divisionOutput_source (d : Nat) (ports : Tape → K)
    (portsInjective : Function.Injective ports) (quotient remainder : Tape)
    (notSourceQuotient : Tape.lookupOutput ≠ quotient)
    (notSourceRemainder : Tape.lookupOutput ≠ remainder)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) :
    divisionOutput d ports quotient remainder base n sourceSuffix quotientSuffix remainderSuffix
      (ports .lookupOutput) = encodeWord 0 ++ sourceSuffix := by
  exact MachineFixedDivMod.unaryTapes_source _ _ _
    (fun h => notSourceQuotient (portsInjective h))
    (fun h => notSourceRemainder (portsInjective h)) _ _ _ _ _ _ _

@[simp] theorem divisionOutput_quotient (d : Nat) (ports : Tape → K)
    (portsInjective : Function.Injective ports) (quotient remainder : Tape)
    (distinct : quotient ≠ remainder) (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) :
    divisionOutput d ports quotient remainder base n sourceSuffix quotientSuffix remainderSuffix
      (ports quotient) = encodeWord (n / degree d) ++ quotientSuffix := by
  exact MachineFixedDivMod.unaryTapes_quotient _ _ _
    (fun h => distinct (portsInjective h)) _ _ _ _ _ _ _

@[simp] theorem divisionOutput_remainder (d : Nat) (ports : Tape → K)
    (quotient remainder : Tape) (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) :
    divisionOutput d ports quotient remainder base n sourceSuffix quotientSuffix remainderSuffix
      (ports remainder) = encodeWord (n % degree d) ++ remainderSuffix := by
  exact MachineFixedDivMod.unaryTapes_remainder _ _ _ _ _ _ _ _ _ _

theorem divisionOutput_other (d : Nat) (ports : Tape → K) (quotient remainder : Tape)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool) (other : K)
    (notSource : other ≠ ports .lookupOutput) (notQuotient : other ≠ ports quotient)
    (notRemainder : other ≠ ports remainder) :
    divisionOutput d ports quotient remainder base n sourceSuffix quotientSuffix remainderSuffix
      other = base other := by
  exact MachineFixedDivMod.unaryTapes_other _ _ _ other notSource notQuotient notRemainder
    _ _ _ _ _ _ _

def firstDivisionInTime {d : Nat} (positive : 0 < d) (H : Table (cloudSize d) d)
    (ports : Tape → K) (portsInjective : Function.Injective ports)
    (labels : Label d → Λ) (exit : Option Λ)
    (target : Λ → TM2.Stmt (fun _ : K => Bool) Λ (State ρ d))
    (atProgram : ∀ label, target (labels label) = statement positive H ports labels exit label)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base (ports .lookupOutput) = encodeWord n ++ sourceSuffix)
    (quotientInput : base (ports .quotientFirst) = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base (ports .remainderFirst) = encodeWord 0 ++ remainderSuffix)
    (ambient : ρ) (control : Control d) (register : Option Bool) :
    StateTransition.EvalsToInTime (TM2.step target)
      ⟨some (labels .firstScan), divisionState positive ambient control register, base⟩
      (some ⟨some (labels .clearQuery), divisionState positive ambient
        (receiveFirst control (MachineFixedDivMod.residue (degree d)
          (Nat.mul_pos positive positive) n)) none,
        divisionOutput d ports .quotientFirst .remainderFirst base n
          sourceSuffix quotientSuffix remainderSuffix⟩) (n + 2) where
  steps := n + 2
  evals_in_steps := firstDivisionTrace positive H ports portsInjective labels exit target atProgram
    base n sourceSuffix quotientSuffix remainderSuffix sourceInput quotientInput remainderInput
    ambient control register
  steps_le_m := Nat.le_refl _

def secondDivisionInTime {d : Nat} (positive : 0 < d) (H : Table (cloudSize d) d)
    (ports : Tape → K) (portsInjective : Function.Injective ports)
    (labels : Label d → Λ) (exit : Option Λ)
    (target : Λ → TM2.Stmt (fun _ : K => Bool) Λ (State ρ d))
    (atProgram : ∀ label, target (labels label) = statement positive H ports labels exit label)
    (base : K → List Bool) (n : Nat)
    (sourceSuffix quotientSuffix remainderSuffix : List Bool)
    (sourceInput : base (ports .lookupOutput) = encodeWord n ++ sourceSuffix)
    (quotientInput : base (ports .quotientSecond) = encodeWord 0 ++ quotientSuffix)
    (remainderInput : base (ports .remainderSecond) = encodeWord 0 ++ remainderSuffix)
    (ambient : ρ) (control : Control d) (register : Option Bool) :
    StateTransition.EvalsToInTime (TM2.step target)
      ⟨some (labels .secondScan), divisionState positive ambient control register, base⟩
      (some ⟨some (labels (.outputEmit (PCP.AlphabetTable.Emitter.labelAt 3 _ 0 .entry))),
        divisionState positive ambient
          (receiveSecond H control (MachineFixedDivMod.residue (degree d)
            (Nat.mul_pos positive positive) n)) none,
        divisionOutput d ports .quotientSecond .remainderSecond base n
          sourceSuffix quotientSuffix remainderSuffix⟩) (n + 2) where
  steps := n + 2
  evals_in_steps := secondDivisionTrace positive H ports portsInjective labels exit target atProgram
    base n sourceSuffix quotientSuffix remainderSuffix sourceInput quotientInput remainderInput
    ambient control register
  steps_le_m := Nat.le_refl _

end MaxCutGames.Foundations.Complexity.MachineExpanderRow

end OAI