[1]
A. O. Ignat'ev, “Bounds for the Periods of Periodic Solutions of Ordinary Differential Equations”, Ukr. Mat. Zhurn., vol. 67, no. 11, pp. 1569–1573, Nov. 2015, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2090