Vasylyshyn PB, Klyus IS, Ptashnik BI. Multipoint problem for hyperbolic equations with variable coefficients. Ukr. Mat. Zhurn. [Internet]. 1996Nov.25 [cited 2024Nov.24];48(11):1468-76. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/5200