proposition: Lemma head_apps : forall n (us : Tes n) t, head (apps t us) = head t.
proof: Proof. induction n; intros us t. VOtac. refl. VSntac us. simpl. rewrite apps_app. simpl. apply IHn. Qed.
imports: Coq(FSets Structures.OrderedType) CoLoR(LogicUtil BoolUtil VecUtil FSetUtil NatUtil RelUtil SN SetUtil)