1. GENERAL NECESSARY CONDITIONS FOR OPTIMIZATION PROBLEMS
2. L. S. Pontryagin, V. G. Boltyanskii, R. V. Gamkrelidze, E. F. Mishchenko, The mathematical theory of optimal processes, Translated from the Russian by K. N. Trirogoff; edited by L. W. Neustadt, Interscience Publishers John Wiley & Sons, Inc. New York-London, 1962, 269–271, and pp. 303-314MR01660370102.32001
3. The Problem of Bounded Space Coordinates as a Problem of Hestenes
4. On control problems with bounded state variables