Tunç, Cemil, and Sultan Erdur. “On the Existence of Periodic Solutions to Certain Non-Linear Differential Equations of Third Order: On the Existence of Periodic Solutions”. Proceedings of the Pakistan Academy of Sciences: A. Physical and Computational Sciences 54, no. 2 (April 29, 2021): 207–218. Accessed November 9, 2024. https://ppaspk.org/index.php/PPAS-A/article/view/251.