Definition erasePerm (m : mem) : mem.

(* Specifications: *)
Lemma erasePerm_Perm : forall m b ofs k , (Mem.valid_block m b -> permission_at (erasePerm m) b ofs k = Some Freeable) /\ (~Mem.valid_block m b -> permission_at (erasePerm m) b ofs k = None).
Lemma erasePerm_V : forall m b ofs k, Mem.valid_block m b -> permission_at (erasePerm m) b ofs k = Some Freeable.
Lemma erasePerm_I : forall m b ofs k, ~ Mem.valid_block m b -> permission_at (erasePerm m) b ofs k = None.