NedokisV. A., SamoilenkoA. M., and TeplinskyY. V. “Truncation Method for Countable-Point Boundary-Value Problems in the Space of Bounded Number Sequences”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, no. 9, Sept. 2004, pp. 1203-30, https://umj.imath.kiev.ua/index.php/umj/article/view/3836.