Goal:
    A : Type  P : list A → list A → A → A → Type  Q : list A → A → Type
  ============================
   (All2_fold P [] [] × All_fold Q [] × All_fold Q [])


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