1. A. P. Balachandran, E. Ercoless, G. Morandi, and A. M. Srivastava,Int. J. Mod. Phys. B,4, No. 14 (1990).
2. P. W. Anderson,Int. J. Mod. Phys. B,4, 181 (1990).
3. V. M. Zharkov,Teor. Mat. Fiz.,60, 404 (1984);77, 107 (1988).
4. A. A. Abrikosov, L. P. Gorkov, and I. E. Dzyaloshinski,Methods of Quantum Field Theory in Statistical Physics, Englewood Cliffs (1963).
5. Yu. A. Izyumov and Yu. N. Skryabin,Statistical Mechanics of Magnetically Ordered Systems [in Russian], Nauka, Moscow (1987).