1. The Theory of Sound;Rayleigh,1877
2. Introduction to Nonlinear Differential and Integral Equations;Davis,1962
3. Perturbation Methods;Nayfeh,1973
4. Nonlinear Oscillations;Nayfeh,1979
5. Averaging using elliptic functions: Approximation of limit cycles;Coppola;Acta Mechanica,1990