-- Mathlib/Computability/TMToPartrec.lean
theorem tr_ret_respects (k v s) : ∃ b₂,
    TrCfg (stepRet k v) b₂ ∧
      Reaches₁ (TM2.step tr)
        ⟨some (Λ'.ret (trCont k)), s, K'.elim (trList v) [] [] (trContStack k)⟩ b₂

Proof state:
fs : Code
as : List ℕ
k : Cont
a_ih✝ :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
v : List ℕ
s : Option Γ'
s' : Cfg'
h₁ : TrCfg (stepNormal fs (Cont.cons₂ v k) as) s'
h₂ :
  Reaches₁ (TM2.step tr)
    { l := some (trNormal fs (trCont (Cont.cons₂ v k))), var := none,
      stk := elim (trList as) [] [] (trContStack (Cont.cons₂ v k)) }
    s'
⊢ main ≠ rev ∧ aux ≠ rev ∧ main ≠ aux

Tactic:
decide

Result:
no goals

Proof state:
case cons₁.intro.intro.refine_2
fs : Code
as : List ℕ
k : Cont
a_ih✝ :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
v : List ℕ
s : Option Γ'
s' : Cfg'
h₁ : TrCfg (stepNormal fs (Cont.cons₂ v k) as) s'
h₂ :
  Reaches₁ (TM2.step tr)
    { l := some (trNormal fs (trCont (Cont.cons₂ v k))), var := none,
      stk := elim (trList as) [] [] (trContStack (Cont.cons₂ v k)) }
    s'
⊢ TransGen (fun a b => b ∈ TM2.step tr a)
    {
      l :=
        some
          (move₂ (fun s => decide (s = Γ'.consₗ)) stack main
            (move₂ (fun x => false) aux stack (trNormal fs (trCont k).cons₂))),
      var := none,
      stk :=
        update (update (elim (trList v) [] [] (trContStack (Cont.cons₁ fs as k))) main (none.elim id List.cons [])) aux
          (elim (trList v) [] [] (trContStack (Cont.cons₁ fs as k)) main ++
            elim (trList v) [] [] (trContStack (Cont.cons₁ fs as k)) aux) }
    s'

Tactic:
simp only [TM2.step, Option.mem_def, Option.elim, id_eq, elim_update_main, elim_main, elim_aux,
  List.append_nil, elim_update_aux]

Result:
case cons₁.intro.intro.refine_2
fs : Code
as : List ℕ
k : Cont
a_ih✝ :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
v : List ℕ
s : Option Γ'
s' : Cfg'
h₁ : TrCfg (stepNormal fs (Cont.cons₂ v k) as) s'
h₂ :
  Reaches₁ (TM2.step tr)
    { l := some (trNormal fs (trCont (Cont.cons₂ v k))), var := none,
      stk := elim (trList as) [] [] (trContStack (Cont.cons₂ v k)) }
    s'
⊢ TransGen
    (fun a b =>
      (match a with
        | { l := none, var := var, stk := stk } => none
        | { l := some l, var := v, stk := S } => some (TM2.stepAux (tr l) v S)) =
        some b)
    {
      l :=
        some
          (move₂ (fun s => decide (s = Γ'.consₗ)) stack main
            (move₂ (fun x => false) aux stack (trNormal fs (trCont k).cons₂))),
      var := none, stk := elim [] [] (trList v) (trContStack (Cont.cons₁ fs as k)) }
    s'

Proof state:
case pos.intro.intro
f : Code
k : Cont
IH :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
v : List ℕ
s : Option Γ'
h : v.headI = 0
this : natEnd (trList v).head?.iget = true ∧ (trList v).tail = trList v.tail
c : Cfg'
h₁ : TrCfg (stepRet k v.tail) c
h₂ :
  Reaches₁ (TM2.step tr)
    { l := some (Λ'.ret (trCont k)), var := (trList v).head?, stk := elim (trList v.tail) [] [] (trContStack k) } c
⊢ TransGen (fun a b => b ∈ TM2.step tr a)
    { l := some (bif true then Λ'.ret (trCont k) else Λ'.clear natEnd main (trNormal f (Cont'.fix f (trCont k)))),
      var := (trList v).head?, stk := elim (trList v.tail) [] [] (trContStack (Cont.fix f k)) }
    c

Tactic:
exact h₂

Result:
no goals

Proof state:
case comp.intro.intro
f : Code
k : Cont
a_ih✝ :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
v : List ℕ
s : Option Γ'
s' : Cfg'
h₁ : TrCfg (stepNormal f k v) s'
h₂ :
  Reaches₁ (TM2.step tr) { l := some (trNormal f (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
    s'
⊢ ∃ b₂,
    TrCfg (stepRet (Cont.comp f k) v) b₂ ∧
      Reaches₁ (TM2.step tr)
        { l := some (Λ'.ret (trCont (Cont.comp f k))), var := s,
          stk := elim (trList v) [] [] (trContStack (Cont.comp f k)) }
        b₂

Tactic:
exact ⟨_, h₁, TransGen.head rfl h₂⟩

Result:
no goals

Proof state:
case cons.succ
f : Code
k : Cont
IH :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
s : Option Γ'
tail✝ : List ℕ
n : ℕ
⊢ if ((n + 1) :: tail✝).headI = 0 then
    natEnd (trList ((n + 1) :: tail✝)).head?.iget = true ∧
      (trList ((n + 1) :: tail✝)).tail = trList ((n + 1) :: tail✝).tail
  else
    natEnd (trList ((n + 1) :: tail✝)).head?.iget = false ∧
      (trList ((n + 1) :: tail✝)).tail =
        (trNat ((n + 1) :: tail✝).headI).tail ++ Γ'.cons :: trList ((n + 1) :: tail✝).tail

Tactic:
rw [trList, List.headI, trNat, Nat.cast_succ, Num.add_one, Num.succ, List.tail]

Result:
case cons.succ
f : Code
k : Cont
IH :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
s : Option Γ'
tail✝ : List ℕ
n : ℕ
⊢ if n + 1 = 0 then
    natEnd (trNum (Num.pos (↑n).succ') ++ Γ'.cons :: trList tail✝).head?.iget = true ∧
      (trNum (Num.pos (↑n).succ') ++ Γ'.cons :: trList tail✝).tail = trList tail✝
  else
    natEnd (trNum (Num.pos (↑n).succ') ++ Γ'.cons :: trList tail✝).head?.iget = false ∧
      (trNum (Num.pos (↑n).succ') ++ Γ'.cons :: trList tail✝).tail =
        (trNum (Num.pos (↑n).succ')).tail ++ Γ'.cons :: trList tail✝

Proof state:
case pos.intro.intro
f : Code
k : Cont
IH :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
v : List ℕ
s : Option Γ'
h : v.headI = 0
this : natEnd (trList v).head?.iget = true ∧ (trList v).tail = trList v.tail
c : Cfg'
h₁ : TrCfg (stepRet k v.tail) c
h₂ :
  Reaches₁ (TM2.step tr)
    { l := some (Λ'.ret (trCont k)), var := (trList v).head?, stk := elim (trList v.tail) [] [] (trContStack k) } c
⊢ TransGen (fun a b => b ∈ TM2.step tr a)
    (TM2.stepAux
      (pop' main
        (goto fun s =>
          bif natEnd s.iget then Λ'.ret (trCont k) else Λ'.clear natEnd main (trNormal f (Cont'.fix f (trCont k)))))
      s (elim (trList v) [] [] (trContStack (Cont.fix f k))))
    c

Tactic:
simp only [pop', TM2.stepAux, elim_main, this, elim_update_main]

Result:
case pos.intro.intro
f : Code
k : Cont
IH :
  ∀ (v : List ℕ) (s : Option Γ'),
    ∃ b₂,
      TrCfg (stepRet k v) b₂ ∧
        Reaches₁ (TM2.step tr) { l := some (Λ'.ret (trCont k)), var := s, stk := elim (trList v) [] [] (trContStack k) }
          b₂
v : List ℕ
s : Option Γ'
h : v.headI = 0
this : natEnd (trList v).head?.iget = true ∧ (trList v).tail = trList v.tail
c : Cfg'
h₁ : TrCfg (stepRet k v.tail) c
h₂ :
  Reaches₁ (TM2.step tr)
    { l := some (Λ'.ret (trCont k)), var := (trList v).head?, stk := elim (trList v.tail) [] [] (trContStack k) } c
⊢ TransGen (fun a b => b ∈ TM2.step tr a)
    { l := some (bif true then Λ'.ret (trCont k) else Λ'.clear natEnd main (trNormal f (Cont'.fix f (trCont k)))),
      var := (trList v).head?, stk := elim (trList v.tail) [] [] (trContStack (Cont.fix f k)) }
    c