Starun, I. I., and N. I. ShkiI. “Linear Singularly Perturbed Systems”. Ukrains’kyi Matematychnyi Zhurnal 54, no. 12 (December 25, 2002): 1688-1693. Accessed May 12, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4207.