(* 
  Find the list of booleans associated with an element,
  return the empty list if the element does not exists
*)
Fixpoint find_code (a : A) (l : code) {struct l} : list bool :=
  match l with
  | nil => nil
  | (b, c) :: l1 =>
      match eqA_dec a b with
      | left _ => c
      | right _ => find_code a l1
      end
  end.

Theorem not_in_find_map : forall p a b, (forall l, ~ In (a, l) p) -> find_code a (map (fun v : A * list bool => match v with | (a1, b1) => (a1, b :: b1) end) p) = nil.