Katriel, Guy. “Uniqueness of Periodic Solutions for Asymptotically Linear Duffing Equations With Strong Forcing”. Topological Methods in Nonlinear Analysis 12, no. 2 (December 1, 1998): 263–274. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.1998.041.