Definition RDOnly_fwd (m1 m1':mem) B :=
  forall b (Hb: B b = true), readonly m1 b m1'.

(* Specifications: *)
Lemma RDOnly_fwd_trans m1 m2 m3 B: RDOnly_fwd m1 m2 B -> RDOnly_fwd m2 m3 B -> RDOnly_fwd m1 m3 B.