Samoilenko, A. M. “Asymptotic Method for the Investigation of M-Frequency Oscillation Systems”. Ukrains’kyi Matematychnyi Zhurnal 50, no. 10 (October 25, 1998): 1366–1387. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4823.