ELNAZAROV, A. A.; SAMOILENKO, A. M. On invariant tori of countable systems of differential equations with delay. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 51, n. 9, p. 1292–1295, 1999. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4726. Acesso em: 5 dec. 2025.