IGNAT'EV, A. O. On the existence of Lyapunov functions in problems of stability of integral sets. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 7, p. 932–941, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5886. Acesso em: 7 apr. 2025.