Maistrenko, Yu. L., and O. V. Popovich. “Existence and Stability of Periodic Solutions for Chains of Connected Oscillators”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 7 (July 25, 1997): 943–950. Accessed May 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5085.