1. Oscillations in Planar Dynamic Systems;Mickens,1996
2. Nonlinear Oscillations;Nayfeh,1979
3. Non-linear Oscillations;Hagedorn,1988
4. Asymptotic Methods in the Theory of Nonlinear Oscillations;Bogoliubov,1963
5. Comments on the method of harmonic-balance;Mickens;J. Sound Vib.,1984