1. Duffing, G., Erzwungene Schwingungen bei veränderlicher Eigenfrequenz und ihre technische Bedeutung, Braunschweig: Vieweg, 1918.
2. Stoker, J. J., Nonlinear Vibrations in Mechanical and Electrical Systems, 2nd ed., New York: Interscience Publ., 1950.
3. Kozlov, V. V., Methods of Qualitative Analysis in the Dynamics of a Rigid Body, Izhevsk: R&C Dynamics, Institute of Computer Science, 2000 (Russian).
4. Guckenheimer, J. and Holmes, Ph., Nonlinear Oscillations, Dynamical Systems, and Bifurcations of Vector Fields, New York: Springer, 1983.
5. Morozov, A. D., Resonances, Cycles and Chaos in Quasi-Conservative Systems, Izhevsk: R&C Dynamics, 2005 (Russian).