E. S. Balla and I. I. Markush, “On asymptotic solution of the mixed problem for a hyperbolic delay equation ”, Ukr. Mat. Zhurn., vol. 23, no. 4, pp. 437–453, Jun. 1971, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/8578