Kaplun, Y. I., Samoilenko, A. M., & Samoilenko, V. G. (2002). Singularly Perturbed Equations with Impulse Action. Ukrains’kyi Matematychnyi Zhurnal, 54(8), 1089-1009. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4149