1. L. D. Landau, J. Phys. USSR, 5, 71–90 (1941).
2. I. M. Khalatnikov, An Introduction to the Theory of Superfluidity [in Russian], URSS, Moscow (1965); English transl., Addison-Wesley, Redwood City, Calif. (1988).
3. N. N. Bogoliubov, J. Phys. USSR, 11, 23–32 (1947).
4. N. N. Bogoliubov, “Quasi-averages in problems of statistical mechanics,” Preprint No. D-781, Joint Inst. Nucl. Res., Dubna (1961); Selected Works in Statistical Physics, Moscow State Univ., Moscow (1979), pp. 193–269.
5. N. Bogolubov, Phys., 26Suppl. 1, S1–S16 (1960).