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3. For a review of investigations of correlated electron systems in the limitd=∞ see Vollhardt, D., In: Correlated electron systems (Lect. Notes for the 9th Jerusalem Winter School for Theoretical Physics), Emery, V.J. (ed.). Singapore: World Scientific (to be published)
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5. Janiš, V.: Z. Phys. B83, 227 (1991)