1. L. S. Pontryagin, V. G. Boltyanskij, R. V. Gamkrelidze, and E. F. Mishchenko, The Mathematical Theory of Optimal Processes [in Russian], Nauka, Moscow (1961); English transl.: Pergamon Press, Oxford etc. (1964).
2. V. I. Plotnikov, “Necessary and sufficient optimality conditions and uniqueness conditions for optimizing functions for control systems of general type” [in Russian], Izv. AN SSSR. Ser. Mat. 36, No. 6, 652–679 (1972); English transl.: Math. USSR, Izv. 6, 649–676 (1973).
3. J. L. Lions, Optimal Control of Systems Governed by Partial Differential Equations, Springer, Berlin etc. (1971).
4. A. I. Egorov, Optimal Control of Thermal and Diffusion Processes [in Russian], Nauka, Moscow (1978).
5. F. P. Vasil’ev, Methods for Solving Extremal Problems [in Russian], Nauka, Moscow (1981).