Goal:
  
  A : Type
  p : A → bool
  x : A
  l : list A
  IHl : forallb p (List.rev l) = forallb p l
  ============================
   (forallb p (List.rev l) && p x = forallb p (List.rev l) && p x)


DEBUG:Going to execute:
trivial with eq_true