Definition ghost_hist (sh : share) (h : hist_part) g :=
own(RA := ref_PCM map_disj_PCM) g (Some (sh, h), None) NoneP.

Lemma ghost_hist_join : forall sh1 sh2 sh h1 h2 p (Hsh : sepalg.join sh1 sh2 sh)
(Hsh1 : sh1 <> Share.bot) (Hsh2 : sh2 <> Share.bot),
ghost_hist sh1 h1 p * ghost_hist sh2 h2 p = !!(disjoint h1 h2) && ghost_hist sh (map_add h1 h2) p.