Definition mem_forward (m1 m2:mem) :=
  forall b, Mem.valid_block m1 b ->
    (Mem.valid_block m2 b
     /\ (forall ofs p, Mem.perm m2 b ofs Max p -> Mem.perm m1 b ofs Max p)
     (*/\ readonly m1 b m2*)).

Lemma lessdef_hastype: forall v v' (V:Val.lessdef v v') T, Val.has_type v' T -> Val.has_type v T.