1. Investigation of the behaviour of the integral curves of a system of two differential equations in the neighborhood of a singular points;Andreev;Transl. AMS,1958
2. Theory of Bifurcations of Dynamic Systems on a Plane;Andronov,1967
3. On the number of limit cycles which appear with the variation of coefficients from an equilibrium position of focus or center type;Bautin;Mat. Sb.,1952
4. Réversibilité et classification des centres nilpotents;Berthier;Ann. Inst. Fourier (Grenoble),1994
5. Une approche au problème du centre-foyer de Poincaré;Briskin;C. R. Acad. Sci. Paris Sér. I Math.,1998