Definition hist_incl (h : hist_part) l := forall t e, h t = Some e -> nth_error l t = Some e.
Definition hist_list (h : hist_part) l := forall t e, h t = Some e <-> nth_error l t = Some e.

Lemma hist_ref_join : forall sh h l p, sh <> Share.bot ->
ghost_hist sh h p * ghost_ref l p =
EX h' : hist_part, !!(hist_list h' l /\ hist_sub sh h h') && ghost_hist_ref sh h h' p.