Samoilenko , A. M. “Investigation of a Discrete Dynamical System in the Vicinity of Quasi-Periodic Trajectory ”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 12 (December 4, 1992): 1702–1711. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8195.