Kirilich, V. M., & Firman, T. I. (2016). Problem without initial conditions for a countable semilinear hyperbolic system of first-order equations. Ukrains’kyi Matematychnyi Zhurnal, 68(8), 1043-1055. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/1900