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sgl_prologue13

Definition

by Henry Yuen · Jul 29, 2026 · Mathlib c5ea003 (Lean v4.30.0)

Definition code
import Definitions.Def_sgl_dig_costs
import Definitions.Def_sgl_clock_poly

/-!
# The prologue, with the polynomial clock

Ten roles: three inputs, the clock, the guide, the counter, the seed, the
ping-pong pair, and an idle partner for the normalising walks.  The four
working tapes are none of them — the loop needs those virgin, and the surest
way to hand them over virgin is never to name them here.

The composition is six stages.  The clock's stage is the machine from
`clockPoly_exists`, whose role indices are this prologue's under a relabeling;
everything else is a published setup machine.
-/

namespace SipserGacsLautemann

variable {tapes : Nat}

set_option maxHeartbeats 4000000 in
set_option synthInstance.maxHeartbeats 1000000 in
/-- **The prologue.**  Roles: `0‥2` inputs, `3` clock, `4` guide, `5` counter,
`6` seed, `7, 8` ping-pong, `9` idle. -/
theorem prologue13_exists (idx : Fin 10 → Fin tapes)
    (hinj : Function.Injective idx) (κ d : Nat) :
    ∃ (S : Type) (_ : Fintype S) (M : TypedMachine tapes S),
      ∀ (T : Fin tapes → Tape) (x0 x1 x2 : List TapeSymbol),
        (∀ c ∈ x0, c ≠ TapeSymbol.blank) →
        (∀ c ∈ x1, c ≠ TapeSymbol.blank) →
        (∀ c ∈ x2, c ≠ TapeSymbol.blank) →
        T (idx 0) = cellsTape [] x0 →
        T (idx 1) = cellsTape [] x1 →
        T (idx 2) = cellsTape [] x2 →
        (∀ k : Fin 10, 3 ≤ k.val → T (idx k) = cellsTape [] []) →
        ∃ cost : Nat,
          cost ≤ 110 * ((κ + 1) *
              (x2.length + (x2.length + (x1.length + x0.length)) + 2)
                ^ (d + 1))
            + 100 * (x2.length + (x2.length + (x1.length + x0.length)) + 2)
            + 300 ∧
          HaltsExactly M (M.startCfg T) cost true ∧
          (((M.step^[cost]) (M.startCfg T)).tape) (idx 0) =
            cellsTape [TapeSymbol.blank] (x0 ++ [TapeSymbol.blank]) ∧
          (((M.step^[cost]) (M.startCfg T)).tape) (idx 1) =
            cellsTape [TapeSymbol.blank] (x1 ++ [TapeSymbol.blank]) ∧
          (((M.step^[cost]) (M.startCfg T)).tape) (idx 2) =
            cellsTape [TapeSymbol.blank] (x2 ++ [TapeSymbol.blank]) ∧
          (((M.step^[cost]) (M.startCfg T)).tape) (idx 3) =
            cellsTape (List.replicate
              ((x2.length + (x2.length + (x1.length + x0.length)) + 1)
                + (κ + 1) *
                  (x2.length + (x2.length + (x1.length + x0.length)) + 1)
                    ^ d)
              (TapeSymbol.bit true) ++ TapeSymbol.blank :: []) [] ∧
          (((M.step^[cost]) (M.startCfg T)).tape) (idx 4) =
            cellsTape []
              (List.replicate (x2.length + 1) (TapeSymbol.bit true) ++
                [TapeSymbol.blank]) ∧
          (((M.step^[cost]) (M.startCfg T)).tape) (idx 5) =
            cellsTape (List.replicate (x2.length + 2) TapeSymbol.blank) [] ∧
          (∀ j, (∀ i : Fin 10, j ≠ idx i) →
            (((M.step^[cost]) (M.startCfg T)).tape) j = T j) := by
  classical
  have hne : ∀ a b : Fin 10, a ≠ b → idx a ≠ idx b :=
    fun a b hab h => hab (hinj h)
  -- the clock stage's machine, on relabeled roles
  set cpIdx : Fin 7 → Fin tapes := fun k =>
    idx (match k with
      | 0 => 0 | 1 => 1 | 2 => 2 | 3 => 6 | 4 => 7 | 5 => 8 | 6 => 3)
    with hcpIdx
  have hcpInj : Function.Injective cpIdx := by
    intro a b hab
    rw [hcpIdx] at hab
    have := hinj hab
    fin_cases a <;> fin_cases b <;> simp_all
  obtain ⟨SC, instC, CP, hCP⟩ := clockPoly_exists cpIdx hcpInj κ d
  letI := instC
  refine ⟨_, ?_, (inputPrep (idx 0) (idx 9)).andThen fun _ =>
    (inputPrep (idx 1) (idx 9)).andThen fun _ =>
      (inputPrep (idx 2) (idx 9)).andThen fun _ =>
        (prepTape (idx 4)).andThen fun _ =>
          CP.andThen fun _ =>
            guideSetup (idx 2) (idx 4) (idx 5), ?_⟩
  · letI i5 : Fintype (stateOf (guideSetup (idx 2) (idx 4) (idx 5))) :=
      inferInstance
    letI i4 : Fintype (stateOf (CP.andThen fun _ =>
      guideSetup (idx 2) (idx 4) (idx 5))) := inferInstance
    letI i3 : Fintype (stateOf ((prepTape (idx 4)).andThen fun _ =>
      CP.andThen fun _ => guideSetup (idx 2) (idx 4) (idx 5))) := inferInstance
    letI i2 : Fintype (stateOf ((inputPrep (idx 2) (idx 9)).andThen fun _ =>
      (prepTape (idx 4)).andThen fun _ =>
        CP.andThen fun _ => guideSetup (idx 2) (idx 4) (idx 5))) :=
      inferInstance
    letI i1 : Fintype (stateOf ((inputPrep (idx 1) (idx 9)).andThen fun _ =>
      (inputPrep (idx 2) (idx 9)).andThen fun _ =>
        (prepTape (idx 4)).andThen fun _ =>
          CP.andThen fun _ => guideSetup (idx 2) (idx 4) (idx 5))) :=
      inferInstance
    exact inferInstance
  intro T x0 x1 x2 hn0 hn1 hn2 hx0 hx1 hx2 hvirgin
  -- stage 1..3: the inputs
  obtain ⟨c1, hb1, g1, t1⟩ := inputPrep_specB (idx 0) (idx 9)
    (hne 0 9 (by decide)) x0 T hn0 hx0
  set F1 := Function.update T (idx 0)
    (cellsTape [TapeSymbol.blank] (x0 ++ [TapeSymbol.blank])) with hF1
  obtain ⟨c2, hb2, g2, t2⟩ := inputPrep_specB (idx 1) (idx 9)
    (hne 1 9 (by decide)) x1 F1 hn1
    (by rw [hF1, Function.update_of_ne (hne 1 0 (by decide))]; exact hx1)
  set F2 := Function.update F1 (idx 1)
    (cellsTape [TapeSymbol.blank] (x1 ++ [TapeSymbol.blank])) with hF2
  obtain ⟨c3, hb3, g3, t3⟩ := inputPrep_specB (idx 2) (idx 9)
    (hne 2 9 (by decide)) x2 F2 hn2
    (by rw [hF2, Function.update_of_ne (hne 2 1 (by decide)), hF1,
      Function.update_of_ne (hne 2 0 (by decide))]; exact hx2)
  set F3 := Function.update F2 (idx 2)
    (cellsTape [TapeSymbol.blank] (x2 ++ [TapeSymbol.blank])) with hF3
  have hF3v : ∀ j, j ≠ idx 0 → j ≠ idx 1 → j ≠ idx 2 → F3 j = T j := by
    intro j h0 h1 h2
    rw [hF3, Function.update_of_ne h2, hF2, Function.update_of_ne h1, hF1,
      Function.update_of_ne h0]
  -- stage 4: the guide's origin marker
  obtain ⟨g4, t4⟩ := prepTape_spec (idx 4) F3 []
    (by rw [hF3v _ (hne 4 0 (by decide)) (hne 4 1 (by decide))
      (hne 4 2 (by decide))]; exact hvirgin 4 (by decide))
  set F4 := Function.update F3 (idx 4)
    (cellsTape [TapeSymbol.blank] []) with hF4
  have hF4v : ∀ j, j ≠ idx 0 → j ≠ idx 1 → j ≠ idx 2 → j ≠ idx 4 →
      F4 j = T j := by
    intro j h0 h1 h2 h4
    rw [hF4, Function.update_of_ne h4]
    exact hF3v j h0 h1 h2
  have hF4i0 : F4 (idx 0) = cellsTape [TapeSymbol.blank]
      (x0 ++ [TapeSymbol.blank]) := by
    rw [hF4, Function.update_of_ne (hne 0 4 (by decide)), hF3,
      Function.update_of_ne (hne 0 2 (by decide)), hF2,
      Function.update_of_ne (hne 0 1 (by decide)), hF1, Function.update_self]
  have hF4i1 : F4 (idx 1) = cellsTape [TapeSymbol.blank]
      (x1 ++ [TapeSymbol.blank]) := by
    rw [hF4, Function.update_of_ne (hne 1 4 (by decide)), hF3,
      Function.update_of_ne (hne 1 2 (by decide)), hF2, Function.update_self]
  have hF4i2 : F4 (idx 2) = cellsTape [TapeSymbol.blank]
      (x2 ++ [TapeSymbol.blank]) := by
    rw [hF4, Function.update_of_ne (hne 2 4 (by decide)), hF3,
      Function.update_self]
  -- stage 5: the polynomial clock
  have hcp0 : cpIdx 0 = idx 0 := rfl
  have hcp1 : cpIdx 1 = idx 1 := rfl
  have hcp2 : cpIdx 2 = idx 2 := rfl
  have hcp3 : cpIdx 3 = idx 6 := rfl
  have hcp4 : cpIdx 4 = idx 7 := rfl
  have hcp5 : cpIdx 5 = idx 8 := rfl
  have hcp6 : cpIdx 6 = idx 3 := rfl
  obtain ⟨c5, hb5, g5, eclk, e0, e1, e2, hCPo⟩ := hCP F4 x0 x1 x2 [] [] []
    [] [] [] hn0 hn1 hn2
    (by rw [hcp0, hF4i0])
    (by rw [hcp1, hF4i1])
    (by rw [hcp2, hF4i2])
    (by rw [hcp3, hF4v _ (hne 6 0 (by decide)) (hne 6 1 (by decide))
      (hne 6 2 (by decide)) (hne 6 4 (by decide))]
        exact hvirgin 6 (by decide))
    (by rw [hcp4, hF4v _ (hne 7 0 (by decide)) (hne 7 1 (by decide))
      (hne 7 2 (by decide)) (hne 7 4 (by decide))]
        exact hvirgin 7 (by decide))
    (by rw [hcp5, hF4v _ (hne 8 0 (by decide)) (hne 8 1 (by decide))
      (hne 8 2 (by decide)) (hne 8 4 (by decide))]
        exact hvirgin 8 (by decide))
    (by rw [hcp6, hF4v _ (hne 3 0 (by decide)) (hne 3 1 (by decide))
      (hne 3 2 (by decide)) (hne 3 4 (by decide))]
        exact hvirgin 3 (by decide))
  set F5 := ((CP.step^[c5]) (CP.startCfg F4)).tape with hF5
  rw [hcp0] at e0
  rw [hcp1] at e1
  rw [hcp2] at e2
  rw [hcp6] at eclk
  have hF5v : ∀ j, j ≠ idx 0 → j ≠ idx 1 → j ≠ idx 2 → j ≠ idx 3 →
      j ≠ idx 4 → j ≠ idx 6 → j ≠ idx 7 → j ≠ idx 8 → F5 j = T j := by
    intro j h0 h1 h2 h3 h4 h6 h7 h8
    rw [hCPo j (by
      intro i
      fin_cases i <;>
        simp only [hcp0, hcp1, hcp2, hcp3, hcp4, hcp5, hcp6] <;>
        assumption)]
    exact hF4v j h0 h1 h2 h4
  -- stage 6: the guide and counter
  obtain ⟨c6, hb6, g6, t6⟩ := guideSetup_specB (idx 2) (idx 4) (idx 5)
    (hne 2 4 (by decide)) (hne 4 5 (by decide)) (hne 2 5 (by decide))
    x2 [] [] F5 hn2 (by rw [e2]; exact hF4i2)
    (by rw [hCPo (idx 4) (by
        intro i
        fin_cases i <;>
          simp only [hcp0, hcp1, hcp2, hcp3, hcp4, hcp5, hcp6] <;>
          first
            | exact hne 4 0 (by decide)
            | exact hne 4 1 (by decide)
            | exact hne 4 2 (by decide)
            | exact hne 4 6 (by decide)
            | exact hne 4 7 (by decide)
            | exact hne 4 8 (by decide)
            | exact hne 4 3 (by decide)), hF4, Function.update_self])
    (by rw [hF5v _ (hne 5 0 (by decide)) (hne 5 1 (by decide))
          (hne 5 2 (by decide)) (hne 5 3 (by decide)) (hne 5 4 (by decide))
          (hne 5 6 (by decide)) (hne 5 7 (by decide)) (hne 5 8 (by decide))]
        exact hvirgin 5 (by decide))
  -- the chain
  have k5 := chainStepC g5 rfl g6
  have k4 := chainStepC g4 t4 k5.1
  have k3 := chainStepC g3 t3 k4.1
  have k2 := chainStepC g2 t2 k3.1
  have k1 := chainStepC g1 t1 k2.1
  have hIR : ∀ {S₁ S₂ : Type} (bb : Bool) (c : TypedConfiguration tapes S₂),
      (TypedConfiguration.inRight (S₁ := S₁) bb c).tape = c.tape :=
    fun _ _ => rfl
  set F6 := Function.update (Function.update F5 (idx 5)
    (cellsTape (List.replicate (x2.length + 2) TapeSymbol.blank) []))
    (idx 4) (cellsTape []
      (List.replicate (x2.length + 1) (TapeSymbol.bit true) ++
        [TapeSymbol.blank])) with hF6
  have hfin : ((((inputPrep (idx 0) (idx 9)).andThen fun _ =>
      (inputPrep (idx 1) (idx 9)).andThen fun _ =>
        (inputPrep (idx 2) (idx 9)).andThen fun _ =>
          (prepTape (idx 4)).andThen fun _ =>
            CP.andThen fun _ =>
              guideSetup (idx 2) (idx 4) (idx 5)).step^[
        c1 + 1 + (c2 + 1 + (c3 + 1 + (3 + 1 + (c5 + 1 + c6))))])
      (((inputPrep (idx 0) (idx 9)).andThen fun _ =>
        (inputPrep (idx 1) (idx 9)).andThen fun _ =>
          (inputPrep (idx 2) (idx 9)).andThen fun _ =>
            (prepTape (idx 4)).andThen fun _ =>
              CP.andThen fun _ =>
                guideSetup (idx 2) (idx 4) (idx 5)).startCfg T)).tape =
      F6 := by
    rw [k1.2, hIR, k2.2, hIR, k3.2, hIR, k4.2, hIR, k5.2, hIR, t6, hF6]
  refine ⟨_, ?_, k1.1, ?_, ?_, ?_, ?_, ?_, ?_, ?_⟩
  · -- the cost
    have hb5' := hb5
    omega
  · rw [hfin, hF6, Function.update_of_ne (hne 0 4 (by decide)),
      Function.update_of_ne (hne 0 5 (by decide))]
    exact e0.trans hF4i0
  · rw [hfin, hF6, Function.update_of_ne (hne 1 4 (by decide)),
      Function.update_of_ne (hne 1 5 (by decide))]
    exact e1.trans hF4i1
  · rw [hfin, hF6, Function.update_of_ne (hne 2 4 (by decide)),
      Function.update_of_ne (hne 2 5 (by decide))]
    exact e2.trans hF4i2
  · rw [hfin, hF6, Function.update_of_ne (hne 3 4 (by decide)),
      Function.update_of_ne (hne 3 5 (by decide))]
    exact eclk
  · rw [hfin, hF6, Function.update_self]
  · rw [hfin, hF6, Function.update_of_ne (Ne.symm (hne 4 5 (by decide))),
      Function.update_self]
  · intro j hj
    rw [hfin, hF6, Function.update_of_ne (hj 4), Function.update_of_ne (hj 5)]
    exact hF5v j (hj 0) (hj 1) (hj 2) (hj 3) (hj 4) (hj 6) (hj 7) (hj 8)

end SipserGacsLautemann

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