[1] BOURBAKI N.: Topologie générale. chap. I & II, 2nd ed., A. S. et I, Paris, 1951.

[2] CODDINGTON E. A., LEVINSON N.: Theory of Ordinary Differential Equations. McGraw-Hill, New York, 1955. MR 0069338 | Zbl 0064.33002

[3] HÁJEK O.: Critical points of dynamical systems. CMUC 5, 3 (1964). MR 0177402

[4] HÁJEK O.: Sections of dynamical systems in $E^2$. to appear in Czechoslovak Mathematical Journal. MR 0176181

[5] HÁJEK O.: Extension of sections of local dynamical systems. ibid.

[6] NIEMYCKIJ V. V., STEPANOV V. V.: Qualitative Theory of Differential Equations. (in Russian), 2nd ed., Gostechizdat, Moscow - Leningrad, 1953.

[7] WHYBURN G. T.: Analytic Topology. AMS Coll. Publ., 1942. MR 0007095 | Zbl 0061.39301