1. Theory und Anwendung der Directen Methode von Ljapunov in (German);Hahn,1959
2. Some Nonlinear Problems in the Theory of Automatic Control;Lure'e,1957
3. Stability of Nonlinear Regulated Systems;Letov,1961
4. The Variable Gradient Method for Generating Liapunov Functions;Shultz;AIEE Transactions,1962
5. Asymptotic Behavior and Stability Problems in Ordinary Differential Equations;Cesari,1959