Tsvetkov, E.L. (1993) “Smoothness of generalized solutions of the third boundary-value problem for an elliptic differential-difference equation”, Ukrains’kyi Matematychnyi Zhurnal, 45(8), pp. 1140–1150. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5911 (Accessed: 10 April 2025).