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


DEBUG:Going to execute:
match goal with
           | |- _ → _ => intro; t_tauto_intuit
           | |- _ => t_reduce; t_solver
           end