Pelyukh, G.P. (2002) “On the Existence of Periodic Solutions of Nonlinear Difference Equations”, Ukrains’kyi Matematychnyi Zhurnal, 54(12), pp. 1626–1633. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4201 (Accessed: 7 April 2025).