theorem Th20:
  g + ZeroLC G = ZeroLC G
  proof
    Carrier ZeroLC(G)={}G by RLVECT_2:def 5;
    then {}G = g+Carrier ZeroLC(G) by Th8
            .= Carrier(g+ZeroLC(G)) by Th16;
    hence thesis by RLVECT_2:def 5;
  end;
