VITRYCHENKO, I. E. On the functional polystability of certain essentially nonlinear nonautonomous differential systems. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 52, n. 2, p. 197–207, 2000. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4408. Acesso em: 6 dec. 2025.