Goal:
  
  A : Type
  P : A → Type
  p : A → bool
  x : A
  l : list A
  p0 : P x
  X : All P l
  IHX : ∀ p : A → bool, (∀ x : A, P x → p x) → forallb p l
  H : ∀ x : A, P x → p x
  ============================
   (is_true (p x))


DEBUG:Going to execute:
match reverse goal with
           | |- ?X1 => <Coq.Init.Tauto.is_unit_or_eq> flags X1; constructor 1
           | H:?X1 |- _ => <Coq.Init.Tauto.is_empty> flags X1; elim H
           | _ => Ltac.assumption
           end