(** Helper lemmas to reason about - the "code is tail of" property - correct translation of labels. *)
Definition tail_nolabel (k c: code) : Prop :=
is_tail k c /\ forall lbl, find_label lbl c = find_label lbl k.

Lemma tail_nolabel_trans:
forall c1 c2 c3, tail_nolabel c2 c3 -> tail_nolabel c1 c2 -> tail_nolabel c1 c3.