1. N. N. Bogolyubov, Quasiaverages in Problems of Statistical Mechanics [in Russian], Preprint JINR 788, Dubna (1961).
2. L. Reatto and G. V. Chester, Phys. Rev.,155, 88 (1967).
3. E. B. Sonin, Zh. Éksp. Teor. Fiz.,59, 1416 (1970).
4. G. Lasher, Phys. Rev.,172, 224 (1968).
5. V. L. Berezinskii, Zh. Éksp. Teor. Fiz.,59, 907 (1970); Zh. Éksp. Teor. Fiz.,61, 1144 (1971).