1. V. I. Arnold, V. V. Kozlov -A. I. Neishtadt,Dynamical systems III, VINITI, Moscow (1985); English translation in Springer-Verlag, New York, Heidelberg, Berlin (1988).
2. V. Benci,Periodic solutions of Lagrangian systems on a compact manifold, J. Diff. Equat.,63 (1986), pp. 135–161.
3. S. V. Bolotin,The existence of homoclinic motions, Vestnik Moskov. Univ., Ser. I, Matem., Mekhan.,6 (1983), pp. 98–103 (Russian); English transl, in Moscow Univ. Math. Boll.,38 (1983), pp. 117–123.
4. S. V. Bolotin -V. V. Kozlov,On the asymptotic solutions of the equations of dynamics, Vestnik Moskov. Univ., Ser. I, Matem., Mekhan.,4 (1980), pp. 84–89 (Russian); English transl. in Moscow Univ. Math. Boll.,35 (1980), pp. 82–88.
5. S. A. Chaplygin,On the motion of heavy bodies in an incompressible fluid, Collected papers 1, Izd-vo Akad. Nauk SSSR, Leningrad (1933), pp. 133–150 (Russian).