1. M. Caubergh, Limit cycles near vector fields of center type, Thesis, Limburgs Universitair Centrum, Diepenbeek, Belgium, 2004
2. F. Dumortier, R. Roussarie, Abelian integrals and limit cycles, 2004, submitted for publication
3. Chebychev Systems and the Versal Unfolding of a Cusp of Order n;Marděsić,1998
4. On the number of limit cycles which appear by perturbation of separatrix loop of planar vector fields;Roussarie;Bol. Soc. Bras. Mat.,1986
5. Bifurcations of Planar Vector Fields and Hilbert's Sixteenth Problem;Roussarie,1998