Remark find_label_add_delta_ranges:
  forall lbl c before after, find_label lbl (add_delta_ranges before after c) = find_label lbl c.

Lemma find_label_match_rec: forall lbl c' c tc, match_code c tc -> find_label lbl c = Some c' -> exists before after tc', find_label lbl tc = Some (add_delta_ranges before after tc') /\ match_code c' tc'.