Goal:
  
  A : Type
  p : nat → A → bool
  q : nat → A → bool
  n : nat
  l : list A
  hpq : ∀ (i : nat) (x : A), p i x → q i x
  ============================
   (alli p n l → alli q n l)


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