VasylyshynP. B., and PtashnikB. I. “A Multipoint Problem for Partial Integro-Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 50, no. 9, Sept. 1998, pp. 1155–1168, https://umj.imath.kiev.ua/index.php/umj/article/view/4832.