1. N. N. Bogolyubov, Selected Works in 3 vols. (Nauk. Dumka, Kiev, 1971) [in Russian].
2. A. A. Belavin et al., Zh. Eksp. Teor. Fiz. 56, 264 (1969) [Sov. Phys. JETP 29, 145 (1969)].
3. A. O. Caldeira and A. J. Leggett, Phys. A 121, 587 (1983); Ann. Phys. 149, 374 (1983); Phys. Rev. Lett. 46, 211 (1981); Phys. Rev. Lett. 48, 1571 (1982).
4. N. G. van Kampen, Stochastic Processes in Physics and Chemistry (North-Holland, Amsterdam, 1981).
5. C. W. Gardiner, Quantum Noise (Springer, Berlin, 1991).