
theorem
  for x,y be Complex holds |.x+y.|*|.x+y.| <= 2*|.x.|*|.x.| + 2*|.y.|*|.
  y.| & |.x.|*|.x.| <= 2*|.x-y.|*|.x-y.| + 2*|.y.|*|.y.| by Lm21;
