Definition nolabel (s: statement) : Prop :=
  forall k, find_label lbl s k = None.Fixpoint nolabel_list (sl: list statement) : Prop :=
  match sl with
  | nil => True
  | s1 :: sl' => nolabel s1 /\ nolabel_list sl'
  end.

Lemma makeif_nolabel: forall a s1 s2, nolabel s1 -> nolabel s2 -> nolabel (makeif a s1 s2).