M. V. Moroz, “On the Existence of Periodic Solutions of a System of Two Differential Equations with Pulse Influence”, Ukr. Mat. Zhurn., vol. 54, no. 1, pp. 133–137, Jan. 2002, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4047