proposition: Lemma not_Rh_app_neutral u v w : neutral u -> ~ App u v ->Rh w.
proof: Proof. intros u_neu r; inversion r; clear r. destruct H. destruct u; inversion H; auto. inversion H. inversion H; clear H. destruct (rule_ok H1) as [f [n [ls i]]]; subst; clear H1. rewrite subs_apps in H0. simpl in H0. apply (f_equal head) in H0. revert u_neu H0. rewrite head_apps. destruct u; simpl; fo. discr. rewrite <- H0 in u_neu. hyp. Qed.
imports: Coq(Morphisms Basics Lia) CoLoR(LogicUtil RelUtil VecOrd VecUtil LAlpha)