(** * Relating two memory states. *)
(** ** Memory extensions *)
(**  A store [m2] extends a store [m1] if [m2] can be obtained from [m1] by relaxing the permissions of [m1] (for instance, allocating larger blocks) and replacing some of the [Vundef] values stored in [m1] by more defined values stored in [m2] at the same addresses. *)
Parameter extends: mem -> mem -> Prop.

Axiom loadbytes_extends:
forall m1 m2 b ofs len bytes1,
extends m1 m2 ->
loadbytes m1 b ofs len = Some bytes1 ->
exists bytes2, loadbytes m2 b ofs len = Some bytes2
/\ list_forall2 memval_lessdef bytes1 bytes2.