(** A range of bytes, with full permissions and unspecified contents. *)
Program Definition range (b: block) (lo hi: Z) : massert := {|
m_pred := fun m =>
0 <= lo /\ hi <= Ptrofs.modulus
/\ (forall i k p, lo <= i < hi -> Mem.perm m b i k p);
m_footprint := fun b' ofs' => b' = b /\ lo <= ofs' < hi
|}.
Next Obligation.
split; auto. split; auto. intros. eapply Mem.perm_unchanged_on; eauto. simpl; auto.
Qed.
Next Obligation.
apply Mem.perm_valid_block with ofs Cur Freeable; auto.
Qed.

Lemma range_drop_left:
forall b lo hi P mid m,
lo <= mid <= hi ->
m |= range b lo hi ** P ->
m |= range b mid hi ** P.