Definition smvalid_src (mu : SM_Injection) m1 :=
  forall b1, DOM mu b1 -> Memory.Mem.valid_block m1 b1.Definition smvalid_tgt (mu : SM_Injection) m2 :=
  forall b2, RNG mu b2 -> Memory.Mem.valid_block m2 b2.

Lemma extern_incr_trans: forall mu mu' mu'' (Inc: extern_incr mu mu') (Inc': extern_incr mu' mu''), extern_incr mu mu''.