Opaque Mem.storebytes.

Lemma mem_free_obs_perm:
forall f m m' m2 m2' lo hi b1 b2
(Hmem_obs_eq: mem_obs_eq f m m')
(Hf: f b1 = Some b2)
(Hfree: Mem.free m b1 lo hi = Some m2)
(Hfree': Mem.free m' b2 lo hi = Some m2') b0 b3 ofs
(Hf0: f b0 = Some b3),
permissions.permission_at m2 b0 ofs Cur =
permissions.permission_at m2' b3 ofs Cur.