1. J. Friedel, Nuovo Cimento Suppl. 12, 1861 (1958).
2. P. W. Anderson, Phys. Rev. 124, 41 (1961).
3. See various articles, in: “Magnetism; A Treatise on Modern Theory and Materials, ” H. Suhl, ed., Academic Press, New York (1973), Vol. V.
4. J. R. Schrieffer and P. A. Wolf, Phys. Rev. 149, 491 (1966).
5. B. Coqblin and J. R. Schrieffer, Phys. Rev. 185 847 (1969).