1. V. I. Arnold, Geometrical Methods in the Theory of Ordinary Differential Equations, Springer-Verlag, New York/Berlin.
2. Théorème de Newton pour les fonctions de classe Cr;Barbançon;Ann. Sci. École Norm. Sup.,1972
3. On the number of limit cycles appearing with variations of coefficients from an equilibrium state of the type of a focus or a center;Bautin;Mat. Sb.,1952
4. Hilbert's 16th problem for quadratic systems and cyclicity of elementary graphics;Dumortier;Nonlinearity,1996
5. Hilbert's 16th problem for quadratic vector fields;Dumortier;J. Differential Equations,1994