for V being VectSp of F_Complex
for f being diagReR+0valued hermitan-Form of V
for v, w being Element of V holds |.(f . ((v + w),(v + w))).| + |.(f . ((v - w),(v - w))).| = (2 * |.(f . (v,v)).|) + (2 * |.(f . (w,w)).|)