1. I. P. Bazarov, Statistical Theory of the Crystal State [in Russian], Moscow State University (1972).
2. V. I. Zubov, Ann. Phys. (Leipzig),32, 93 (1975).
3. É. V. Gevorkyan, Teor. Mat. Fiz.,26, 282 (1976).
4. A. A. Vlasov, Many-Body Theory [in Russian], Gostekhizdat, Moscow (1950).
5. V. A. Golovko, Izv. Vyssh. Uchebn. Zaved. Fiz., No. 2, 67 (1979).