Goal:
    A : Type  P : list A → list A → A → A → Type  Q : list A → A → Type
  ============================
   (All_fold Q [])


DEBUG:Going to execute:
match goal with
           | |- ?X1 → ?X2 => intro
           | |- ¬ _ => unfold not at 1; intro
           end
Level 0: Backtrace:

No matching clauses for match.