aesop
case h_2
C : Type u_1
τ : Type u_2
inst✝⁴ : Fold C τ
inst✝³ : LeanColls.ToList C τ
inst✝² : ToList C τ
inst✝¹ : LeanColls.ToList C τ
inst✝ : ToList C τ
f : τ → Bool
c : C
f' : Unit → τ → Except Unit Unit
hf' : (fun x x => if f x = true then Except.error () else Except.ok ()) = f'
this : foldM c f' () = Except.error () ↔ (toList c).any f = true
x✝ : Except Unit Unit
heq✝ : foldM c f' () = Except.error PUnit.unit
⊢ (toList c).any f = true
no goals