Vasylyshyn, P. B., and B. I. Ptashnik. “A Multipoint Problem for Partial Integro-Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 50, no. 9 (September 25, 1998): 1155–1168. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4832.