GorodniiM. F. “Existence of Solutions of Boundary-Value Problems Corresponding to a Certain Difference Equation in a Banach Space”. Ukrains’kyi Matematychnyi Zhurnal 45, no. 3 (March 25, 1993): 431–435. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5826.