References
- Cesari , L. 1963 . Asymptotic Behavior and Stability Problems in Ordinary Differential Equations , Berlin : Springer-Verlag .
- Cronin , J. 1964 . Fixed Points and Topological Degree in Nonlinear Analysis , American Mathematical Society .
- Lefschetz , S. Differential Equations: Geometric Theory , New York : Interscience Publishers .