Theorem: Turing.PartrecToTM2.pred_ok
File: Mathlib/Computability/TMToPartrec.lean

Proof steps:
state_before: q₁ q₂ : Λ'
s : Option Γ'
v : List ℕ
c d : List Γ'
⊢ ∃ s',
    Reaches₁ (TM2.step tr) { l := some (q₁.pred q₂), var := s, stk := elim (trList v) [] c d }
      (Nat.rec { l := some q₁, var := s', stk := elim (trList v.tail) [] c d }
        (fun n x => { l := some q₂, var := s', stk := elim (trList (n :: v.tail)) [] c d }) v.headI)
state_after: case nil
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
⊢ ∃ s',
    Reaches₁ (TM2.step tr) { l := some (q₁.pred q₂), var := s, stk := elim (trList []) [] c d }
      (Nat.rec { l := some q₁, var := s', stk := elim (trList [].tail) [] c d }
        (fun n x => { l := some q₂, var := s', stk := elim (trList (n :: [].tail)) [] c d }) [].headI)

case cons.zero
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
⊢ ∃ s',
    Reaches₁ (TM2.step tr) { l := some (q₁.pred q₂), var := s, stk := elim (trList (0 :: v)) [] c d }
      (Nat.rec { l := some q₁, var := s', stk := elim (trList (0 :: v).tail) [] c d }
        (fun n x => { l := some q₂, var := s', stk := elim (trList (n :: (0 :: v).tail)) [] c d }) (0 :: v).headI)

case cons.succ
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
⊢ ∃ s',
    Reaches₁ (TM2.step tr) { l := some (q₁.pred q₂), var := s, stk := elim (trList ((n + 1) :: v)) [] c d }
      (Nat.rec { l := some q₁, var := s', stk := elim (trList ((n + 1) :: v).tail) [] c d }
        (fun n_1 x => { l := some q₂, var := s', stk := elim (trList (n_1 :: ((n + 1) :: v).tail)) [] c d })
        ((n + 1) :: v).headI)
tactic: rcases v with (_ | ⟨_ | n, v⟩)
state_before: case cons.succ
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
⊢ ∃ s',
    Reaches₁ (TM2.step tr) { l := some (q₁.pred q₂), var := s, stk := elim (trList ((n + 1) :: v)) [] c d }
      (Nat.rec { l := some q₁, var := s', stk := elim (trList ((n + 1) :: v).tail) [] c d }
        (fun n_1 x => { l := some q₂, var := s', stk := elim (trList (n_1 :: ((n + 1) :: v).tail)) [] c d })
        ((n + 1) :: v).headI)
state_after: case cons.succ
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
⊢ Reaches₁ (TM2.step tr) { l := some (q₁.pred q₂), var := s, stk := elim (trList ((n + 1) :: v)) [] c d }
    (Nat.rec { l := some q₁, var := none, stk := elim (trList ((n + 1) :: v).tail) [] c d }
      (fun n_1 x => { l := some q₂, var := none, stk := elim (trList (n_1 :: ((n + 1) :: v).tail)) [] c d })
      ((n + 1) :: v).headI)
tactic: refine ⟨none, ?_⟩
state_before: case cons.succ
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
⊢ Reaches₁ (TM2.step tr) { l := some (q₁.pred q₂), var := s, stk := elim (trList ((n + 1) :: v)) [] c d }
    (Nat.rec { l := some q₁, var := none, stk := elim (trList ((n + 1) :: v).tail) [] c d }
      (fun n_1 x => { l := some q₂, var := none, stk := elim (trList (n_1 :: ((n + 1) :: v).tail)) [] c d })
      ((n + 1) :: v).headI)
state_after: case cons.succ
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
⊢ Reaches₁ (TM2.step tr)
    { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum (↑n).succ' ++ Γ'.cons :: trList v) [] c d }
    { l := some q₂, var := none,
      stk :=
        elim
          ((match ↑n with
            | Num.zero => []
            | Num.pos n => trPosNum n) ++
            Γ'.cons :: trList v)
          [] c d }
tactic: simp only [TM2.step, trList, trNat.eq_1, trNum, Nat.cast_succ, Num.add_one, Num.succ,
    List.tail_cons, List.headI_cons]
state_before: case cons.succ
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
⊢ Reaches₁ (TM2.step tr)
    { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum (↑n).succ' ++ Γ'.cons :: trList v) [] c d }
    { l := some q₂, var := none,
      stk :=
        elim
          ((match ↑n with
            | Num.zero => []
            | Num.pos n => trPosNum n) ++
            Γ'.cons :: trList v)
          [] c d }
state_after: case cons.succ.zero
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
⊢ Reaches₁ (TM2.step tr)
    { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum Num.zero.succ' ++ Γ'.cons :: trList v) [] c d }
    { l := some q₂, var := none,
      stk :=
        elim
          ((match Num.zero with
            | Num.zero => []
            | Num.pos n => trPosNum n) ++
            Γ'.cons :: trList v)
          [] c d }

case cons.succ.pos
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
a : PosNum
⊢ Reaches₁ (TM2.step tr)
    { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum (Num.pos a).succ' ++ Γ'.cons :: trList v) [] c d }
    { l := some q₂, var := none,
      stk :=
        elim
          ((match Num.pos a with
            | Num.zero => []
            | Num.pos n => trPosNum n) ++
            Γ'.cons :: trList v)
          [] c d }
tactic: cases' (n : Num) with a
state_before: case cons.succ.pos
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
a : PosNum
⊢ Reaches₁ (TM2.step tr)
    { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum (Num.pos a).succ' ++ Γ'.cons :: trList v) [] c d }
    { l := some q₂, var := none,
      stk :=
        elim
          ((match Num.pos a with
            | Num.zero => []
            | Num.pos n => trPosNum n) ++
            Γ'.cons :: trList v)
          [] c d }
state_after: case cons.succ.pos
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
a : PosNum
⊢ Reaches₁ (TM2.step tr)
    { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum a.succ ++ Γ'.cons :: trList v) [] c d }
    { l := some q₂, var := none, stk := elim (trPosNum a ++ Γ'.cons :: trList v) [] c d }
tactic: simp only [Num.succ']
state_before: case cons.succ.pos
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
a : PosNum
⊢ Reaches₁ (TM2.step tr)
    { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum a.succ ++ Γ'.cons :: trList v) [] c d }
    { l := some q₂, var := none, stk := elim (trPosNum a ++ Γ'.cons :: trList v) [] c d }
state_after: case cons.succ.pos
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
a : PosNum
⊢ ∀ (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum a) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr)
          { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum a.succ ++ Γ'.cons :: trList v) l₁ c d }
          { l := some (unrev q₂), var := s', stk := elim (l₂' ++ Γ'.cons :: trList v) l₁' c d }
tactic: suffices ∀ l₁, ∃ l₁' l₂' s',
    List.reverseAux l₁ (trPosNum a) = List.reverseAux l₁' l₂' ∧
      Reaches₁ (TM2.step tr)
        ⟨some (q₁.pred q₂), s, K'.elim (trPosNum a.succ ++ Γ'.cons :: trList v) l₁ c d⟩
        ⟨some (unrev q₂), s', K'.elim (l₂' ++ Γ'.cons :: trList v) l₁' c d⟩ by
    obtain ⟨l₁', l₂', s', e, h⟩ := this []
    simp only [List.reverseAux] at e
    refine h.trans ?_
    convert unrev_ok using 2
    simp [e, List.reverseAux_eq]
state_before: case cons.succ.pos
q₁ q₂ : Λ'
s : Option Γ'
c d : List Γ'
v : List ℕ
n : ℕ
a : PosNum
⊢ ∀ (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum a) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr)
          { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum a.succ ++ Γ'.cons :: trList v) l₁ c d }
          { l := some (unrev q₂), var := s', stk := elim (l₂' ++ Γ'.cons :: trList v) l₁' c d }
state_after: case cons.succ.pos.one
q₁ q₂ : Λ'
c d : List Γ'
v : List ℕ
n : ℕ
s : Option Γ'
l₁ : List Γ'
⊢ ∃ l₁' l₂' s',
    l₁.reverseAux (trPosNum PosNum.one) = l₁'.reverseAux l₂' ∧
      Reaches₁ (TM2.step tr)
        { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum PosNum.one.succ ++ Γ'.cons :: trList v) l₁ c d }
        { l := some (unrev q₂), var := s', stk := elim (l₂' ++ Γ'.cons :: trList v) l₁' c d }

case cons.succ.pos.bit1
q₁ q₂ : Λ'
c d : List Γ'
v : List ℕ
n : ℕ
m : PosNum
IH :
  ∀ (s : Option Γ') (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum m) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr)
          { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum m.succ ++ Γ'.cons :: trList v) l₁ c d }
          { l := some (unrev q₂), var := s', stk := elim (l₂' ++ Γ'.cons :: trList v) l₁' c d }
s : Option Γ'
l₁ : List Γ'
⊢ ∃ l₁' l₂' s',
    l₁.reverseAux (trPosNum m.bit1) = l₁'.reverseAux l₂' ∧
      Reaches₁ (TM2.step tr)
        { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum m.bit1.succ ++ Γ'.cons :: trList v) l₁ c d }
        { l := some (unrev q₂), var := s', stk := elim (l₂' ++ Γ'.cons :: trList v) l₁' c d }

case cons.succ.pos.bit0
q₁ q₂ : Λ'
c d : List Γ'
v : List ℕ
n : ℕ
m : PosNum
IH :
  ∀ (s : Option Γ') (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum m) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr)
          { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum m.succ ++ Γ'.cons :: trList v) l₁ c d }
          { l := some (unrev q₂), var := s', stk := elim (l₂' ++ Γ'.cons :: trList v) l₁' c d }
s : Option Γ'
l₁ : List Γ'
⊢ ∃ l₁' l₂' s',
    l₁.reverseAux (trPosNum m.bit0) = l₁'.reverseAux l₂' ∧
      Reaches₁ (TM2.step tr)
        { l := some (q₁.pred q₂), var := s, stk := elim (trPosNum m.bit0.succ ++ Γ'.cons :: trList v) l₁ c d }
        { l := some (unrev q₂), var := s', stk := elim (l₂' ++ Γ'.cons :: trList v) l₁' c d }
tactic: induction' a with m IH m IH generalizing s <;> intro l₁