Require Export VST.veric.base.
Local Open Scope pred.
Notation ghost_approx m := (ghost_fmap (approx (level m)) (approx (level m))).
(* Ownership construction based on "Iris from the ground up", Jung et al. *)
Program Definition ghost_is g: pred rmap :=
fun m => ghost_of m = ghost_approx m g.
Next Obligation.
intros ???? Hg.
rewrite (age1_ghost_of _ _ H), Hg.
pose proof (age_level _ _ H).
rewrite ghost_fmap_fmap, approx_oo_approx', approx'_oo_approx by omega; eauto.
Qed.
Definition Own g: pred rmap := allp noat && ghost_is g.

Lemma Own_op: forall a b c, join a b c -> Own c = Own a * Own b.