1. G. N. Duboshin, Celestial Mechanics. Analytical and Qualitative Methods (Nauka, Moscow, 1964) [in Russian].
2. V. G. Demin, Motion of Artificial Satellite in a Noncentral Gravitational Field (Nauka, Moscow, 1968) [in Russian].
3. V. V. Beletsky, Essays on the Motion of Celestial Bodies (Nauka, Moscow, 1972; Birkhäuser, Basel, 2001).
4. E. P. Aksenov, E. A. Grebenikov, and V. G. Demin, Sov. Astron. 7, 276 (1963).
5. N. S. Koshlyakov, E. B. Gliner, and M. M. Smirnov, Partial Differential Equations of Mathematical Physics (Vysshaya Shkola, Moscow, 1970) [in Russian].