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

theorem Th40:
  (-x).|.y = x.|.(-y)
proof
  thus (-x).|.y = (-(1r*')) * x.|.y by COMPLEX1:30,def 4
    .=((-1r)*')* x.|.y by COMPLEX1:33
    .= x.|.((-1r)*y) by Th36
    .=x.|.(-y) by COMPLEX1:def 4;
end;
