Goal:
    A : Type  P : A → Prop  Q : A → Prop  l : list A  l' : list A
  ============================
   (All P l → All Q l' → #|l| = #|l'| → All2 (λ x y : A, P x ∧ Q y) l l')


DEBUG:Going to execute:
induction l in l' |- *; destruct l'; simpl