I. I. Starun and N. I. ShkiI, “Linear Singularly Perturbed Systems”, Ukr. Mat. Zhurn., vol. 54, no. 12, pp. 1688–1693, Dec. 2002, Accessed: Apr. 09, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4207