1. Alekseev, V.M., Tikhomirov, V.M., and Fomin, S.V., Optimal’noe upravlenie (Optimal Control), Moscow: Nauka, 1979.
2. Vapnyarskii, I.B., Theory of Existence of the Optimal Control in the Boltz Problem, Some of Its Applications, and the Necessary Conditions for Optimality of the Sliding and Special Modes, Zh. Vychisl. Mat. Mat. Fiz., 1967, vol. 7, no. 2, pp. 259–283.
3. Gamkrelidze, R.V., On Optimal Sliding Modes, Dokl. Akad. Nauk SSSR, 1962, vol. 134, no. 6, pp. 1243–1245.
4. Filippov, A.F., On Some Issues of the Theory of Optimal Control, Vestn.Mosk. Gos. Univ., Ser. Mat., 1959, no. 2, pp. 25–32.
5. Krotov, V.F., Discontinuous Solutions of the Variational Problems, Izv. Vyssh. Uchebn. Zaved., Mat., 1960, no. 5 (18), pp. 86–98.