1. R. P. Agarwal and E. Yu. Romanenko, “Stable periodic solutions of difference equations,” Appl. Math. Lett., 11, No. 4, 81–84 (1998).
2. M. Kuczma, B. Choczewski, and R. Ger, Iterative Functional Equations, Cambridge University Press, Cambridge (1990).
3. D. I. Martynyuk, Lectures on the Qualitative Theory of Difference Equations [in Russian], Naukova Dumka, Kiev (1972).
4. G. P. Pelyukh, “On the existence of periodic solutions of nonlinear difference equations,” Ukr. Mat. Zh., 54, No. 12, 1623–1633 (2002); English translation: Ukr. Math. J., 54, No. 12, 1971–1981 (2002).
5. H. P. Pelyukh and O. A. Syvak, “Periodic solutions of the systems of nonlinear functional equations,” Nelin. Kolyv., 16, No. 1, 90–93 (2013); English translation: J. Math. Sci., 197, No. 1, 92–95 (2014).