1. Investigation of the behaviour of the integral curves of a system of two differential equations in the neighbourhood of a singular point;Andreev;Am. Math. Soc.,1958
2. Les cycles limites de Poincaré et la theorie des oscillations auto-entretenues;Andronov;C. R. Acad. Sci. Paris,1929
3. Qualitative Theory of Second Order Dynamic Systems;Andronov,1973
4. N. Bautin, On the number of limit cycles which appear with the variation of coefficients from an equilibrium position of focus or center type, Amer. Math. Soc. Trans. 100 (154)
5. The number of limit cycles of certain polynomial differential equations;Blows;Proc. Roy. Soc. Edinburgh A,1984