  From general considerations of spin-symmetry breaking associated with
(anti-)ferromagnetism in metallic systems with Coulomb repulsion, we obtain
interesting and simple all-order rules involving the ratios of the densities of
states. These are exact for ferromagnetism under reasonable conditions, and
nearly exact for anti-ferromagnetism. In the case of ferromagnetism, the
comparison with the available experimental and theoretical numbers yields
favourable results.
