Goal:
  
  A : Type
  P : A → Prop
  a : A
  l : list A
  p : A → bool
  IHl : ∀ p : A → bool, forallb p l → (∀ x : A, p x → P x) → Forall P l
  H0 : ∀ x : A, p x → P x
  H1 : is_true (p a)
  H2 : is_true (forallb p l)
  ============================
   (P a)


DEBUG:Going to execute:
fun flags =>
             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