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'.