Fixpoint find_label (lbl: label) (c: code) {struct c} : option code :=
  match c with
  | nil => None
  | i1 :: il => if is_label lbl i1 then Some il else find_label lbl il
  end.

(* Specifications: *)
Lemma find_label_tail: forall lbl c c', find_label lbl c = Some c' -> is_tail c' c.
Lemma find_label_incl: forall lbl c c', find_label lbl c = Some c' -> incl c' c.