Klyuchnyk, I. H. “Asymptotic Solutions of a System of Differential Equations With Multiple Turning Point”. Ukrains’kyi Matematychnyi Zhurnal 61, no. 11 (November 25, 2009): 1516–1530. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3118.