Goal:
  
  A : Type
  B : Type
  f : A → B
  a : A
  l : list A
  p : B → bool
  IHl : ∀ (f : A → B) (p : B → bool),
          forallb p (map f l) = forallb (λ x : A, p (f x)) l
  ============================
   (p (f a) && forallb p (map f l) = p (f a) && forallb (λ x : A, p (f x)) l)


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