(* Rather than carry the initial value, let's just write it as the first element in the history. *)
Definition atomic_loc_hist sh p g R (h : hist) := atomic_loc sh p (hist_R g R) * ghost_hist sh h g.

Lemma atomic_loc_hist_isptr : forall sh p g R h,
atomic_loc_hist sh p g R h = !!(isptr p) && atomic_loc_hist sh p g R h.