1. Mori H.: Progr. Theor. Phys.33 (1965) 423.
2. Fick E., Sauermann G.: Quantenstatistik dynamischer Processe, Band IIa. Geest and Portig K.-G., Leipzig, 1985, p. 89.
3. Grabert H.: Projection Operator Techniques in Nonequilibrium Statistical Mechanics. Springer Tracts in Modern Physics 95. Springer, Berlin-Heidelberg-New York, 1982, p. 36.
4. Tokuyama M., Mori H.: Progr. Theor. Phys.55 (1976) 411.
5. Hashitsume N., Shibata F., Shingu M.: J. Stat. Phys.17 (1977) 155.