Proof using.
intros J P.
cofix c.
intros [x s] alJ.
apply W_tl.
- apply always_now in alJ.
assumption.
- apply c.
apply always_invar in alJ.
assumption.
Qed.

(* Specifications: *)
Lemma always_release :
forall (J P : infseq T -> Prop) (s : infseq T), always P s -> release J P s.