-- Mathlib/Data/Seq/Parallel.lean
theorem terminates_parallel.aux :
    ∀ {l : List (Computation α)} {S c},
      c ∈ l → Terminates c → Terminates (corec parallel.aux1 (l, S))

Proof state:
case cons.inl
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c✝ : Computation α
T : c✝.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
S : WSeq (Computation α)
c : Computation α
l : List (Computation α)
IH' : s.think ∈ l → ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
l' : List (Computation α)
e' :
  (match
      List.foldr
        (fun c o =>
          match o with
          | Sum.inl a => Sum.inl a
          | Sum.inr ls =>
            match c.destruct with
            | Sum.inl a => Sum.inl a
            | Sum.inr b => Sum.inr (b :: ls))
        (Sum.inr []) l with
    | Sum.inl a => Sum.inl a
    | Sum.inr ls =>
      match c.destruct with
      | Sum.inl a => Sum.inl a
      | Sum.inr b => Sum.inr (b :: ls)) =
    Sum.inr l'
e : s.think = c
⊢ s ∈ l'

Tactic:
rw [← e] at e'

Result:
case cons.inl
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c✝ : Computation α
T : c✝.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
S : WSeq (Computation α)
c : Computation α
l : List (Computation α)
IH' : s.think ∈ l → ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
l' : List (Computation α)
e' :
  (match
      List.foldr
        (fun c o =>
          match o with
          | Sum.inl a => Sum.inl a
          | Sum.inr ls =>
            match c.destruct with
            | Sum.inl a => Sum.inl a
            | Sum.inr b => Sum.inr (b :: ls))
        (Sum.inr []) l with
    | Sum.inl a => Sum.inl a
    | Sum.inr ls =>
      match s.think.destruct with
      | Sum.inl a => Sum.inl a
      | Sum.inr b => Sum.inr (b :: ls)) =
    Sum.inr l'
e : s.think = c
⊢ s ∈ l'

Proof state:
case intro
α : Type u
l : List (Computation α)
S : WSeq (Computation α)
a : α
e : parallel.aux2 l = Sum.inl a
this : corec parallel.aux1 (l, S) = Pure.pure a
⊢ (Pure.pure a).Terminates

Tactic:
exact ret_terminates a

Result:
no goals

Proof state:
case inl
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c : Computation α
T : c.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
l : List (Computation α)
S : WSeq (Computation α)
m : s.think ∈ l
H1 : ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
a : α
h : parallel.aux2 l = Sum.inl a
⊢ (corec parallel.aux1 (l, S)).Terminates

Tactic:
exact lem1 _ _ ⟨a, h⟩

Result:
no goals

Proof state:
case cons.inr.inr.inr
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c✝ : Computation α
T : c✝.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
S : WSeq (Computation α)
c : Computation α
l : List (Computation α)
IH' : s.think ∈ l → ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
l' : List (Computation α)
m : s.think ∈ l
ls : List (Computation α)
e :
  List.foldr
      (fun c o =>
        match o with
        | Sum.inl a => Sum.inl a
        | Sum.inr ls => rmap (fun c' => c' :: ls) c.destruct)
      (Sum.inr []) l =
    Sum.inr ls
this : s ∈ ls
val✝ : Computation α
h' : val✝ :: ls = l'
⊢ s ∈ l'

Tactic:
rw [← h']

Result:
case cons.inr.inr.inr
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c✝ : Computation α
T : c✝.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
S : WSeq (Computation α)
c : Computation α
l : List (Computation α)
IH' : s.think ∈ l → ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
l' : List (Computation α)
m : s.think ∈ l
ls : List (Computation α)
e :
  List.foldr
      (fun c o =>
        match o with
        | Sum.inl a => Sum.inl a
        | Sum.inr ls => rmap (fun c' => c' :: ls) c.destruct)
      (Sum.inr []) l =
    Sum.inr ls
this : s ∈ ls
val✝ : Computation α
h' : val✝ :: ls = l'
⊢ s ∈ val✝ :: ls

Proof state:
case cons.inr.inr
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c✝ : Computation α
T : c✝.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
S : WSeq (Computation α)
c : Computation α
l : List (Computation α)
IH' : s.think ∈ l → ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
l' : List (Computation α)
m : s.think ∈ l
ls : List (Computation α)
e' :
  (match Sum.inr ls with
    | Sum.inl a => Sum.inl a
    | Sum.inr ls =>
      match c.destruct with
      | Sum.inl a => Sum.inl a
      | Sum.inr b => Sum.inr (b :: ls)) =
    Sum.inr l'
e :
  List.foldr
      (fun c o =>
        match o with
        | Sum.inl a => Sum.inl a
        | Sum.inr ls => rmap (fun c' => c' :: ls) c.destruct)
      (Sum.inr []) l =
    Sum.inr ls
this : s ∈ ls
⊢ s ∈ l'

Tactic:
revert e'

Result:
case cons.inr.inr
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c✝ : Computation α
T : c✝.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
S : WSeq (Computation α)
c : Computation α
l : List (Computation α)
IH' : s.think ∈ l → ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
l' : List (Computation α)
m : s.think ∈ l
ls : List (Computation α)
e :
  List.foldr
      (fun c o =>
        match o with
        | Sum.inl a => Sum.inl a
        | Sum.inr ls => rmap (fun c' => c' :: ls) c.destruct)
      (Sum.inr []) l =
    Sum.inr ls
this : s ∈ ls
⊢ (match Sum.inr ls with
      | Sum.inl a => Sum.inl a
      | Sum.inr ls =>
        match c.destruct with
        | Sum.inl a => Sum.inl a
        | Sum.inr b => Sum.inr (b :: ls)) =
      Sum.inr l' →
    s ∈ l'

Proof state:
α : Type u
lem1 :
  ∀ (l : List (Computation α)) (S : WSeq (Computation α)),
    (∃ a, parallel.aux2 l = Sum.inl a) → (corec parallel.aux1 (l, S)).Terminates
c : Computation α
T : c.Terminates
s : Computation α
IH : ∀ {l : List (Computation α)} {S : WSeq (Computation α)}, s ∈ l → (corec parallel.aux1 (l, S)).Terminates
l : List (Computation α)
S : WSeq (Computation α)
m : s.think ∈ l
H1 : ∀ (l' : List (Computation α)), parallel.aux2 l = Sum.inr l' → s ∈ l'
l' : List (Computation α)
h : parallel.aux2 l = Sum.inr l'
⊢ (match
      match parallel.aux2 l with
      | Sum.inl a => Sum.inl a
      | Sum.inr b =>
        Sum.inr
          (match Seq.destruct S with
          | none => (b, Seq.nil)
          | some (none, S') => (b, S')
          | some (some c, S') => (c :: b, S')) with
    | Sum.inl a => Sum.inl a
    | Sum.inr b => Sum.inr (corec parallel.aux1 b)) =
    Sum.inr ?m.8713

Tactic:
rw [h]

Result:
no goals