LE, N. N. Optimal control of systems with time delays. Vietnam Journal of Mechanics, Hanoi, Vietnam, v. 14, n. 3, p. 13–19, 1992. DOI: 10.15625/0866-7136/10235. Disponível em: https://vjs.ac.vn/index.php/vjmech/article/view/10235. Acesso em: 27 jun. 2022.