(* not useful? *)

Lemma nonreadable_field_at_eq {cs: compspecs} :
forall sh t gfs v v' p,
~ readable_share sh ->
(value_fits (nested_field_type t gfs) v <-> value_fits (nested_field_type t gfs) v') ->
field_at sh t gfs v p = field_at sh t gfs v' p.