1. For a number of reviews on correlation effects in transition metals see e.g.: Electron correlation and magnetism in narrow band systems. Springer series in solid-state science. Moriya, T. (ed.), Vol. 29. Berlin, Heidelberg, New York: Springer-Verlag 1981
2. For a review on strongly correlated valence fluctuating systems see e.g.: Jefferson, J.H., Stevens, K.W.H.: J. Phys. C ?Solid State Physics11, 3919 (1978)
3. Kiel, B., Stollhoff, G., Fulde, P., Stoll, H.: Phys. Lett.87A, 433 (1982)
4. Kiel, B., Stollhoff, G., Weigel, C., Fulde, P., Stoll, H.: Z. Phys. B ? Condensed Matter46, 1 (1982)
5. Stollhoff, G., Fulde, P.: Z. Phys. B ? Condensed Matter26, 257 (1977); ibid.29, 231 (1978)