1. L. S. Pontryagin, V. G. Boltyanskii, R. V. Gamkrelidze, and E. F. Mishchenko, Mathematical Theory of Optimal Processes (Fizmatlit, Moscow, 1961) [in Russian].
2. G. G. Magaril-Il’yaev and V. M. Tikhomirov, Convex Analysis and Its Applications (Librokom, Moscow, 2011) [in Russian].