1. On a theorem of Bendixson;Lefschetz;Bol. Soc. Mat. Mex.,1956
2. Algebraic Geometry;Lefschetz,1953
3. Differential equations;Lefschetz,1964
4. Sur les courbes définies par les équations différentielles;Bendixson;Act Mat.,1901
5. On Frommer's method for studying a singular point of a first order differential equation;Andreiev,1962