4Zhang Zhi-Fen,Li Bao-Yi. High order Melnikov functions and the problem of uniformity in global bifurcation[J] 1992,Annali di Matematica Pura ed Applicata(1):181～212
5R. Roussarie. On the number of limit cycles which appear by perturbation of separatrix loop of planar vector fields[J] 1986,Boletim da Sociedade Brasileira de Matemática(2):67～101
