1. A phase-plane approach to the compensation of saturating servomechanisms;Hopkin;Trans. AIEE.,1951
2. Optimal processes in automatic control systems;Feldbaum;Avtomat. i. Telemekh.,1953
3. Differential equations with a discontinuous forcing term;Bushaw,1952
4. On the bang-bang control problem;Bellman;Quart. Appl. Math.,1955
5. Some mathematical problems arising in connection with the theory of optimal automatic control systems;Pontryagin,1957