1. Non-linear Vibrations;Stoker,1950
2. Non-linear Oscillations;Nayfeh,1979
3. Forced oscillations in nearly sinusoidal systems;Cartwright;J. Inst. Elec. Eng.,1948
4. Bifurcations in the forced van der Pol oscillator;Holmes;Q. appl. Math.,1978
5. Theory of Bifurcations of Dynamical Systems on a Plane;Andronov,1971