Samoilenko, A. M., and Yu. V. Teplinsky. “On the Reducibility of Countable Systems of Linear Difference Equations”.
Ukrains’kyi Matematychnyi Zhurnal, vol. 47, no. 11, Nov. 1995, pp. 1533–1541,
https://umj.imath.kiev.ua/index.php/umj/article/view/5544.