MartynyukD. I., PerestyukN. A., and SamoilenkoA. M. “Reducibility of Nonlinear Almost Periodic Systems of Difference Equations on an Infinite-Dimensional Torus”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 46, no. 9, Sept. 1994, pp. 1216–1223, https://umj.imath.kiev.ua/index.php/umj/article/view/5638.