Beresnevich, V. V., Bernik, V. I., Vasylyshyn, P. B., & Ptashnik, B. I. (1999). A multipoint problem with multiple nodes for linear hyperbolic equations. Ukrains’kyi Matematychnyi Zhurnal, 51(10), 1311–1316. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4729