theorem Th16:
  -(h + g) = -g + -h
proof
  (-g + -h) + (h + g) = -g + -h + h + g by RLVECT_1:def 3
    .= -g + (-h + h) + g by RLVECT_1:def 3
    .= -g + 0_G + g by Def5
    .= -g + g by Def4
    .= 0_G by Def5;
  hence thesis by Th11;
end;
