1. Les Méthods Nouvelles de la Mécanique Célèste;Poincaré,1957
2. Theorie der Transformationgruppen;Lie,1888
3. Dynamical Systems;Birkhoff,1927
4. Local Methods in Nonlinear Differential Equations;Bruno,1989
5. Applied Methods in the Theory of Nonlinear Oscillations;Starzhinskii,1980