VITRYCHENKO, I. E. On the instability of one nonautonomous essentially nonlinear equation of thenth order. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 51, n. 6, p. 835–841, 1999. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4670. Acesso em: 5 dec. 2025.