Gorodnii, M. F., & Romanenko, V. N. (2000). Approximation of a bounded solution of one difference equation with unbounded operator coefficient by solutions of the corresponding boundary-value problems. Ukrains’kyi Matematychnyi Zhurnal, 52(4), 548-552. https://umj.imath.kiev.ua/index.php/umj/article/view/4445