Ignat’evA. O. (1993) “On the existence of Lyapunov functions in problems of stability of integral sets”, Ukrains’kyi Matematychnyi Zhurnal, 45(7), pp. 932–941. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5886 (Accessed: 27July2024).