PELYUKH, G. P. On the Existence of Periodic Solutions of Nonlinear Difference Equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 54, n. 12, p. 1626–1633, 2002. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4201. Acesso em: 7 apr. 2025.