MISAK, V. V. Periodic solutions of differential-difference autonomic systems with one degree of freedom . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 5, p. 111–116, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8448. Acesso em: 6 dec. 2025.