Definition removeUndefs (j l j':meminj):meminj :=
   fun b => match j b with
              None => match l b with
                         None => None | Some (b1,delta1) => j' b
                      end
            | Some(b2,delta2) => Some(b2, delta2)
            end.

Lemma meminij_no_overlap_inject_incr: forall j m (NOV: Mem.meminj_no_overlap j m) k (K:inject_incr k j), Mem.meminj_no_overlap k m.