(*in extern_incr steps, sm_inject_separated_intern_MYB is not needed/trivial, since locBlocksSrc mu b = locBlocksSrc mu' b and locBlocksTgt mu b = locBlocksTgt mu' b*)
Definition sm_valid (mu : SM_Injection) (m1 m2: mem) :=
(forall b1, DOM mu b1 -> Mem.valid_block m1 b1)
/\ (forall b2, RNG mu b2 -> 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''.