BELAN, E. P. Global solutions and invariant tori of difference-differential equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 1, p. 11–24, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4983. Acesso em: 5 dec. 2025.