KirilichV. M., and FirmanT. I. “Problem Without Initial Conditions for a Countable Semilinear Hyperbolic System of First-Order Equations”. Ukrains’kyi Matematychnyi Zhurnal 68, no. 8 (August 25, 2016): 1043-1055. Accessed November 21, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1900.