Kitanov, P. M., and V. A. Plotnikov. “Bogolyubov Theorem for Quasidifferential Equations With Pulses”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 11 (November 25, 1997): 1504–1511. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/5149.