VITRYCHENKO, I. E. On a special critical case of stability of a nonautonomous essentially nonlinear system. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 57, n. 12, p. 1711–1718, 2005. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3721. Acesso em: 11 apr. 2025.