1. Andronov, A., Leontovich, E., Gordon, I., Maier, A.: Qualitative Theory of Second-Order Dynamic Systems. Wiley, New York (1973)
2. Andreev, A., Andreeva, I., Detchenya, L., Makovetskaya, T., Sadovskii, A.: Nilpotent centers of cubic systems. Differ. Equ. 53(8), 1003–1008 (2017)
3. Krivtsov, A.: The ballistic heat equation for a one-dimensional harmonic crystal. Dyn. Proc. Gen. Cont. Struct. 103, 345–358 (2019)
4. Poincare, H.: On Curves Defined by Differential Equations. OGIS, Moscow (1947)
5. Poincare, H.: Les methodes nouvelles de la mecanique celeste, Paris (1892–99)