1. Relaxed Controls and the Dynamics of Control Systems
2. E. A. Barbashin, E. A. Barbašin, Introduction to the theory of stability, Translated from the Russian by Transcripta Service, London. Edited by T. Lukes, Wolters-Noordhoff Publishing, Groningen, 1970, 223–41:87370198.19703
3. Principles of Optimal Control Theory