1. V. A. Zagrebnov, Ann. Phys. (N. Y.),102, 108 (1976).
2. V. A. Zagrebnov, International Symposium on Selected Problems of Statistical Mechanics, Dubna, April 19?22, 1977 (Abstracts), D17-10529, JINR (1977).
3. D. Ruelle, Statistical Mechanics, New York (1969).
4. M. E. Fisher, Arch. Ration. Mech. Anal.,17, 377 (1964).
5. T. Kato, Perturbation Theory for Linear Operators, Springer, Berlin (1966).