(* Lemma subp_later {A} `{agA:  ageable A} (SS: natty A): forall (P Q: pred A), |> (P >=> Q) |-- |> P >=> |> Q. *)

(* Specifications: *)
Lemma extend_unfash {A} {JA: Join A}{PA: Perm_alg A}{SA: Sep_alg A}{AG: ageable A}{XA: Age_alg A} : forall (P: pred nat), boxy extendM (! P).
Hint Resolve @extend_unfash.
Lemma subp_unfash {A} `{Age_alg A}:
forall (P Q : pred nat) (n: nat), (P >=> Q) n -> ( ! P >=> ! Q) n.