(* not useful? *)

(* Lemma nonreadable_data_at_rec_eq {cs: compspecs} : forall sh t v v' p, ~readable_share sh -> field_compatible t nil p -> data_at_rec sh t v p = data_at_rec sh t v' p. *)
Lemma nonreadable_data_at_eq {cs: compspecs}:
forall sh t v v' p, ~readable_share sh ->
(value_fits t v <-> value_fits t v') ->
data_at sh t v p = data_at sh t v' p.