Definition ghost_hist_ref sh (h r : hist_part) g :=
  own(RA := ref_PCM map_disj_PCM) g (Some (sh, h), Some r) NoneP.

(* Specifications: *)
Lemma hist_incl_nil : forall h, hist_incl empty_map h.
Lemma hist_sub_list_incl : forall sh h h' l (Hsub : hist_sub sh h h') (Hlist : hist_list h' l), hist_incl h l.
Lemma hist_sub_Tsh : forall h h', hist_sub Tsh h h' <-> (h = h').