Balanov, Zalman, Fulai Chen, Jing Guo, and Wiesław Krawcewicz. 2021. “Periodic Solutions to Reversible Second Order Autonomous Systems With Commensurate Delays”. Topological Methods in Nonlinear Analysis 59 (2A):475-98. https://doi.org/10.12775/TMNA.2020.039.