Yakovets V. P. “Construction of Asymptotic Solutions of Linear Singularly Disturbed Second-Order System With Degenerations”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 8 (September 8, 1992): 1102-1112. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/8040.