1. 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. (N.S.),1952
2. New Directions in Dynamical Systems;Bedford,1988
3. Bifurcations of limit cycles of a quadratic system with two singular points and two parameters that rotate the field;Cherkas;Differ. Uravn.,1987
4. A family of quadratic polynomial differential systems with invariant algebraic curves of arbitrarily high degree without rational first integrals;Christopher;Proc. Amer. Math. Soc.,2002
5. Perturbation from an elliptic Hamiltonian of degree four. IV. Figure eight-loop;Dumortier;J. Differential Equations,2003