KolesovA. Yu., and RozovN. Kh. 2013. “New Methods for the Investigation of Periodic Solutions in Ring Systems of Unidirectionally Coupled Oscillators”. Ukrains’kyi Matematychnyi Zhurnal 65 (1), 82-102. https://umj.imath.kiev.ua/index.php/umj/article/view/2406.