tr_supports — Mathlib

English

The read-based transition in the one-step simulation is captured by applying the continuation to the head and updating the tape accordingly.

Русский

Переход на основе чтения в одноступенчатом моделировании описывается применением продолжения к_HEAD и обновлением ленты.

LaTeX

$$$$\\operatorname{stepAux}(\\operatorname{read}\\ dec\\ f)\\; v\\; \\operatorname{trTape}'(enc0,L,R) = \\operatorname{stepAux}(f(\\langle L, R.head\\rangle))\\; v\\; \\operatorname{trTape}'(enc0, L, R).$$$$

Lean4

theorem tr_supports [Inhabited Λ] {S : Finset Λ} (ss : Supports M S) : Supports (tr enc dec M) (trSupp M S) :=
  ⟨Finset.mem_biUnion.2 ⟨_, ss.1, Finset.mem_insert_self _ _⟩, fun q h ↦
    by
    suffices
      ∀ q,
        SupportsStmt S q →
          (∀ q' ∈ writes q, q' ∈ trSupp M S) →
            SupportsStmt (trSupp M S) (trNormal dec q) ∧ ∀ q' ∈ writes q, SupportsStmt (trSupp M S) (tr enc dec M q')
      by
      rcases Finset.mem_biUnion.1 h with ⟨l, hl, h⟩
      have := this _ (ss.2 _ hl) fun q' hq ↦ Finset.mem_biUnion.2 ⟨_, hl, Finset.mem_insert_of_mem hq⟩
      rcases Finset.mem_insert.1 h with (rfl | h)
      exacts [this.1, this.2 _ h]
    intro q hs hw
    induction q with
    | move d q IH =>
      unfold writes at hw ⊢
      replace IH := IH hs hw; refine ⟨?_, IH.2⟩
      cases d <;> simp only [trNormal, supportsStmt_move, IH]
    | write f q IH =>
      unfold writes at hw ⊢
      simp only [Finset.mem_image, Finset.mem_union, Finset.mem_univ, true_and] at hw ⊢
      replace IH := IH hs fun q hq ↦ hw q (Or.inr hq)
      refine ⟨supportsStmt_read _ fun a _ s ↦ hw _ (Or.inl ⟨_, rfl⟩), fun q' hq ↦ ?_⟩
      rcases hq with (⟨a, q₂, rfl⟩ | hq)
      · simp only [tr, supportsStmt_write, supportsStmt_move, IH.1]
      · exact IH.2 _ hq
    | load a q IH =>
      unfold writes at hw ⊢
      replace IH := IH hs hw
      exact ⟨supportsStmt_read _ fun _ ↦ IH.1, IH.2⟩
    | branch p q₁ q₂ IH₁ IH₂ =>
      unfold writes at hw ⊢
      simp only [Finset.mem_union] at hw ⊢
      replace IH₁ := IH₁ hs.1 fun q hq ↦ hw q (Or.inl hq)
      replace IH₂ := IH₂ hs.2 fun q hq ↦ hw q (Or.inr hq)
      exact ⟨supportsStmt_read _ fun _ ↦ ⟨IH₁.1, IH₂.1⟩, fun q ↦ Or.rec (IH₁.2 _) (IH₂.2 _)⟩
    | goto l =>
      simp only [writes, Finset.notMem_empty]; refine ⟨?_, fun _ ↦ False.elim⟩
      refine supportsStmt_read _ fun a _ s ↦ ?_
      exact Finset.mem_biUnion.2 ⟨_, hs _ _, Finset.mem_insert_self _ _⟩
    | halt =>
      simp only [writes, Finset.notMem_empty]; refine ⟨?_, fun _ ↦ False.elim⟩
      simp only [SupportsStmt, trNormal]⟩

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