Section GVar.
Context {A : Type}.
Definition ghost_var (sh : share) (v : A) g :=
own(RA := @pos_PCM (discrete_PCM A)) g (Some (sh, v)) NoneP.

Lemma ghost_var_share_join : forall sh1 sh2 sh v p, sepalg.join sh1 sh2 sh ->
sh1 <> Share.bot -> sh2 <> Share.bot ->
ghost_var sh1 v p * ghost_var sh2 v p = ghost_var sh v p.