V. M. Kirilich and T. I. Firman, “Problem without initial conditions for a countable semilinear hyperbolic system of first-order equations”, Ukr. Mat. Zhurn., vol. 68, no. 8, pp. 1043–1055, Aug. 2016, Accessed: Feb. 16, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/1900