Goal:
  
  A : Type
  B : Type
  P : A → B → Type
  Q : A → B → Type
  f : ∀ (x : A) (y : B), P x y → Q x y
  ============================
   (∀ (l : list A) (l' : list B) (a : All2 P l l'),
      map_All2_graph l l' a (map_All2 a))


DEBUG:Going to execute:
let eos := fresh "eos" in
           pose proof CoreTactics.the_end_of_the_section as eos