KlyusI. S., and PtashnikB. I. “A Multipoint Problem for Pseudodifferential Equations”. Ukrains’kyi Matematychnyi Zhurnal 55, no. 1 (January 25, 2003): 22-29. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3884.