Proof using.
intros J P s rl un.
induction un as [s Ps |x s Js IHun IH].
- destruct s as [x s].
unfold not_tl in Ps.
apply release_Cons in rl.
destruct rl as [Psr rl].
contradict Ps.
assumption.
- apply release_Cons in rl.
destruct rl as [Ps rl].
unfold not_tl in Js.
case rl; trivial.
Qed.

(* Specifications: *)
Lemma until_not_release :
forall (J P : infseq T -> Prop) (s : infseq T),
until J P s -> ~ release (~_ J) (~_ P) s.