Ermolaeva, P. G., and V. B. Cherepennikov. “Polynomial Quasisolutions of Linear Second-Order Differential-Difference Equations”. Ukrains’kyi Matematychnyi Zhurnal 60, no. 1 (January 25, 2008): 140–152. Accessed May 2, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3144.