1. Hubbard, J.: Proc. R. Soc. London Ser. A276, 238 (1963); Gutzwiller, M.C.: Phys. Rev. Lett.10, 159 (1063); Kanamori, J.: Prog. Theor. Phys.30, 257 (1963)
2. Proceedings of the International Conference on “Itinerant-Electron Magnetism”. Physica B+C91 (1977); for a review about the theory of the Hubbard model see also Vollhardt, D.: Rev. Mod. Phys.56, 99 (1984)
3. Lieb, E.H., Wu, F.Y.: Phys. Rev. Lett.20, 1445 (1968); Frahm, H., Korepin, V.E.: Phys. Rev. B42, 10533 (1990); Kawakami, N., Yang, S.-K.: Phys. Rev. Lett.65, 2309 (1990)
4. Anderson, P.W.: Phys. Rev. Lett.64, 1839 (1999);65, 2306 (1990)
5. Schulz, H.J.: Proceedings of the Adriatico Research Conference on Strongly Correlated Electron Systems II, Baskaran, G., Ruckenstein, A.E., Tosatti, E., Yu Lu (eds.). Singapore: World Scientific 1991