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 RU_no_overlap: forall m1 m2 j12 (MInj12 : Mem.inject j12 m1 m2) m1' (Fwd1: mem_forward m1 m1') j23 m3 (MInj23 : Mem.inject j23 m2 m3) j' j12' j23' n1' n2' (HeqMKI: mkInjections m1 m1' m2 j12 j23 j' = (j12',j23',n1',n2')), Mem.meminj_no_overlap (removeUndefs j12 j' j12') m1'.