1. Asymptotic Methods in the Theory of Nonlinear Oscillators;Bogoliubov,1961
2. Ordinary and Delay Differential Equations;Driver,1977
3. The method of averaging for differential difference equations of the neutral type;Foduck;Ukraı̈. Mat. Zh.,1968
4. Nonlinear Oscillations, Dynamical Systems, and Bifurcations of Vector Fields;Guckenheimer,1983
5. The method of averaging in equations with retardation;Halanay;Rev. Mat. Pur. Appl. Acad. R.P.R.,1959