Sun, Ji Tao Singular point index problems for time-invariant planar systems. (Chinese) Zbl 0900.34025 Acta Math. Sci. (Chin. Ed.) 15, No. 3, 319-322 (1995). MSC: 34C05 PDFBibTeX XMLCite \textit{J. T. Sun}, Acta Math. Sci. (Chin. Ed.) 15, No. 3, 319--322 (1995; Zbl 0900.34025)
Sun, Ji Tao The qualitative behavior of Liénard systems. (Chinese) Zbl 0900.34033 Acta Math. Sci. (Chin. Ed.) 14, No. 1, 90-95 (1994). MSC: 34C11 34C05 34C25 34D40 PDFBibTeX XMLCite \textit{J. T. Sun}, Acta Math. Sci. (Chin. Ed.) 14, No. 1, 90--95 (1994; Zbl 0900.34033)