Samusenko, P. F. “Asymptotic Integration of Singularly Perturbed Systems of Hyperbolic-Type Partial Differential Equations With Degeneration”. Ukrains’kyi Matematychnyi Zhurnal 63, no. 5 (May 25, 2011): 668-685. Accessed March 29, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2752.