SamoilenkoM. V., and TeplinskyYu. V. 1996. “On Periodic Solutions of Countable Systems of Linear and Quasilinear Difference Equations With Periodic Coefficients”. Ukrains’kyi Matematychnyi Zhurnal 48 (8), 1144-52. https://umj.imath.kiev.ua/index.php/umj/article/view/5258.