Goal:
  
  A : Type
  P : A → Prop
  a : A
  l : list A
  h : Forall P (a :: l)
  IHl : Forall P l → Forall P (List.rev l)
  H1 : P a
  H2 : Forall P l
  ============================
   (Forall P l)


DEBUG:Going to execute:
assumption