theorem Th17:
  (-x) .|. y = x .|. (-y)
proof
  (-x) .|. y = ((-1r)*x) .|. y by CLVECT_1:3
    .= x.|.( (-(1r))*' * y) by Th14
    .= x.|.( (-1r) * y) by COMPLEX1:30,33;
  hence thesis by CLVECT_1:3;
end;
