1. Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables;Abramowitz,1965
2. Monodromy and stability for nilpotent critical points;Álvarez;Internat. J. Bifur. Chaos Appl. Sci. Engrg.,2005
3. Qualitative Theory of Second-Order Dynamic Systems;Andronov,1973
4. The disappearance of the limit cycle in a mode interaction problem with Z2 symmetry;Castro;Nonlinearity,1997
5. The Dulac function for polynomial autonomous systems on a plane;Cherkas;Differ. Uravn.,1997