2YE Yan-qian.Qualitative theory of polynomial differential systems[M].Shanghai:Shanghai Scientific & Technical Publishers,1995.1-618.
3ZHANG Zhi-fen,DING Tong-ren,HUANG Wen-zhao,et al.Qualitative theory of differential equation[M].Beijing:Beijing Scientific & Technical Publishers,1985.1-550.
4杨小京,清华大学学报,1992年,32卷,4期,92页
5李宇寰,组合数学,1988年,182页
6张芷芬,微分方程定性理论,1985年,67,130页
7张锦炎.冯贝叶.常微分方程几何理论与分支问题[M].北京:北京大学出版社,2002.
8Yang Xinan , Zhang Jianfeng. Algebraic classification of polynomial systems in the plane [J ]. Ann of Diff Eqs, 1990,6 (4) : 463 -480.