(* not useful? *)

Lemma mapsto_data_at {cs: compspecs} sh t v v' p :  (* not needed here *)
type_is_by_value t = true ->
type_is_volatile t = false ->
isptr p ->
size_compatible t p ->
align_compatible t p ->
complete_legal_cosu_type t = true ->
JMeq v v' ->
mapsto sh t p v = data_at sh t v' p.