1. Beletskii, V.V., Ocherki o dvizhenii kosmicheskikh tel (Essays on the Motion of Space Bodies), Moscow: Nauka, 1972.
2. Jorba, A. and Simó, C., On Quasiperiodic Perturbations of Elliptic Equilibrium Point, SIAM Journal on Mathematical Analysis, 1996, vol. 27, no. 6, pp. 1704–1737.
3. Kozlov, V.V., Simmetrii, topologiya i rezonansy v gamil’tonovoi mekhanike (Symmetries, Topology, and Resonances in Hamiltonian Mechanics), Izhevsk: Izdvo Udmurtskogo Gos. Univ., 1995.
4. Scheurle, J., Chaotic Solutions of Systems with Almost Periodic Forcing, Zeitschrift fuer Angewandte Mathematik und Physik (ZAMP), 1986, vol. 37, no. 1, pp. 12–26.
5. Meyer, K.R. and Sell, G.R., Melnikov Transforms, Bernoulli Bundles, and Almost Periodic Perturbations, Trans. AMS, 1989, vol. 314, no. 1, pp. 63–105.