1. Hopf bifurcations in nonautonomous systems at points of resonance;Cheng;Sci. Sinica Ser. A,1990
2. Bifurcations of invariant cycles in nonautonomous systems;Qian;Acta Math. Sinica,1983
3. Geometrical Methods in the Theory of Ordinary Differential Equations;Arnold,1983
4. Versal deformations of equivariant vector field for the case of symmetries of order 2 and 3;Horozov,1979
5. A system with three limit cycles appearing in a Hopf bifurcation and dying in a homoclinic bifurcation: The cusp of order 4;Li;J. Differential Equations,1989