Opaque Mem.alloc.
Transparent Mem.free.

Lemma free_access_other:
forall m1 bf lo hi m2, Mem.free m1 bf lo hi = Some m2 ->
forall b ofs k,
b <> bf \/ ofs < lo \/ hi <= ofs ->
access_at m1 (b,ofs) k = access_at m2 (b,ofs) k.