Proof using.
intros P s ioP cnyP.
induction cnyP.
- destruct s as [x s].
apply always_now in ioP.
induction ioP.
* destruct s0 as [x' s0].
apply always_now in H.
unfold not_tl in H0.
contradict H0.
assumption.
* apply always_invar in H.
contradict IHioP.
assumption.
- apply inf_often_invar in ioP.
contradict IHcnyP.
assumption.
Qed.

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