Li, Jing-Wen, and Sui Sun Cheng. “A Priori Bounds for Periodic Solutions of Neutral Differential Equations With Delay”. Tamkang Journal of Mathematics 38, no. 3 (September 30, 2007): 239–246. Accessed July 3, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/76.