reserve a, b, c, d, x, y, z for Complex;

theorem Th30:
  |. x.|.y .| = |.x.|*|.y.|
proof
  thus |.(x.|.y).| =(|.x.|)*(|.y*'.|) by COMPLEX1:65
    .=|.x.|*|.y.| by COMPLEX1:53;
end;
