-- Mathlib/Computability/TMToPartrec.lean
theorem succ_ok {q s n} {c d : List Γ'} :
    Reaches₁ (TM2.step tr) ⟨some (Λ'.succ q), s, K'.elim (trList [n]) [] c d⟩
      ⟨some q, none, K'.elim (trList [n.succ]) [] c d⟩

Proof state:
case pos.bit1.intro.intro.intro.intro
q : Λ'
n : ℕ
c d : List Γ'
m : PosNum
IH :
  ∀ {s : Option Γ'} (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum m.succ) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum m ++ [Γ'.cons]) l₁ c d }
          { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
s : Option Γ'
l₁ l₁' l₂' : List Γ'
s' : Option Γ'
e : (Γ'.bit0 :: l₁).reverseAux (trPosNum m.succ) = l₁'.reverseAux l₂'
h :
  Reaches₁ (TM2.step tr)
    { l := some q.succ, var := ?m.108487, stk := elim (trPosNum m ++ [Γ'.cons]) (Γ'.bit0 :: l₁) c d }
    { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
⊢ { l := some q.succ, var := ?m.108487, stk := elim (trPosNum m ++ [Γ'.cons]) (Γ'.bit0 :: l₁) c d } ∈
    TM2.step tr { l := some q.succ, var := s, stk := elim (trPosNum m.bit1 ++ [Γ'.cons]) l₁ c d }

Tactic:
simp [PosNum.succ, trPosNum]

Result:
case pos.bit1.intro.intro.intro.intro
q : Λ'
n : ℕ
c d : List Γ'
m : PosNum
IH :
  ∀ {s : Option Γ'} (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum m.succ) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum m ++ [Γ'.cons]) l₁ c d }
          { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
s : Option Γ'
l₁ l₁' l₂' : List Γ'
s' : Option Γ'
e : (Γ'.bit0 :: l₁).reverseAux (trPosNum m.succ) = l₁'.reverseAux l₂'
h :
  Reaches₁ (TM2.step tr)
    { l := some q.succ, var := ?m.108487, stk := elim (trPosNum m ++ [Γ'.cons]) (Γ'.bit0 :: l₁) c d }
    { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
⊢ some Γ'.bit1 = ?m.108487

Proof state:
case intro.intro.intro.intro
q : Λ'
s : Option Γ'
n : ℕ
c d : List Γ'
a : PosNum
this :
  ∀ (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum a.succ) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum a ++ [Γ'.cons]) l₁ c d }
          { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
l₁' l₂' : List Γ'
s' : Option Γ'
h :
  Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum a ++ [Γ'.cons]) [] c d }
    { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
e : trPosNum a.succ = l₁'.reverse ++ l₂'
⊢ TransGen (fun a b => b ∈ TM2.step tr a) { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
    { l := some q, var := none, stk := elim (trPosNum a.succ ++ [Γ'.cons]) [] c d }

Tactic:
convert unrev_ok using 2

Result:
case h.e'_2.h.e'_7
q : Λ'
s : Option Γ'
n : ℕ
c d : List Γ'
a : PosNum
this :
  ∀ (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum a.succ) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum a ++ [Γ'.cons]) l₁ c d }
          { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
l₁' l₂' : List Γ'
s' : Option Γ'
h :
  Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum a ++ [Γ'.cons]) [] c d }
    { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
e : trPosNum a.succ = l₁'.reverse ++ l₂'
⊢ elim (trPosNum a.succ ++ [Γ'.cons]) [] c d =
    update (update (elim (l₂' ++ [Γ'.cons]) l₁' c d) rev []) main
      ((elim (l₂' ++ [Γ'.cons]) l₁' c d rev).reverseAux (elim (l₂' ++ [Γ'.cons]) l₁' c d main))

Proof state:
case pos.bit0
q : Λ'
n : ℕ
c d : List Γ'
m : PosNum
a_ih✝ :
  ∀ {s : Option Γ'} (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum m.succ) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum m ++ [Γ'.cons]) l₁ c d }
          { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
s : Option Γ'
l₁ : List Γ'
⊢ ∃ l₁' l₂' s',
    l₁.reverseAux (trPosNum m.bit0.succ) = l₁'.reverseAux l₂' ∧
      Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum m.bit0 ++ [Γ'.cons]) l₁ c d }
        { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }

Tactic:
refine ⟨l₁, _, some Γ'.bit0, rfl, TransGen.single ?_⟩

Result:
case pos.bit0
q : Λ'
n : ℕ
c d : List Γ'
m : PosNum
a_ih✝ :
  ∀ {s : Option Γ'} (l₁ : List Γ'),
    ∃ l₁' l₂' s',
      l₁.reverseAux (trPosNum m.succ) = l₁'.reverseAux l₂' ∧
        Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trPosNum m ++ [Γ'.cons]) l₁ c d }
          { l := some (unrev q), var := s', stk := elim (l₂' ++ [Γ'.cons]) l₁' c d }
s : Option Γ'
l₁ : List Γ'
⊢ { l := some (unrev q), var := some Γ'.bit0, stk := elim (trPosNum m.bit0.succ ++ [Γ'.cons]) l₁ c d } ∈
    TM2.step tr { l := some q.succ, var := s, stk := elim (trPosNum m.bit0 ++ [Γ'.cons]) l₁ c d }

Proof state:
case zero
q : Λ'
s : Option Γ'
n : ℕ
c d : List Γ'
⊢ Reaches₁ (TM2.step tr) { l := some q.succ, var := s, stk := elim (trNum Num.zero ++ [Γ'.cons]) [] c d }
    { l := some q, var := none, stk := elim (trNum Num.zero.succ ++ [Γ'.cons]) [] c d }

Tactic:
refine TransGen.head rfl ?_

Result:
case zero
q : Λ'
s : Option Γ'
n : ℕ
c d : List Γ'
⊢ TransGen (fun a b => b ∈ TM2.step tr a) (TM2.stepAux (tr q.succ) s (elim (trNum Num.zero ++ [Γ'.cons]) [] c d))
    { l := some q, var := none, stk := elim (trNum Num.zero.succ ++ [Γ'.cons]) [] c d }