Definition bytes_writable (loc: address) (size: Z) (phi: rmap) : Prop :=
  forall i, (0 <= i < size) -> writable (adr_add loc i) phi.Definition bytes_readable (loc: address) (size: Z) (phi: rmap) : Prop :=
  forall i, (0 <= i < size) -> readable (adr_add loc i) phi.

Lemma bytes_writable_readable: forall m loc n, bytes_writable m loc n -> bytes_readable m loc n.