RomanenkoO. Yu., and SharkovskyO. M. “Dynamics of Solutions of the Simplest Nonlinear Boundary-Value Problems”. Ukrains’kyi Matematychnyi Zhurnal 51, no. 6 (June 25, 1999): 810–826. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4668.