Nishizawa, Yusuke. “Extended Constant Parts of Becker-Stark’s and Shafer-Fink’s Inequalities”. Tamkang Journal of Mathematics 47, no. 4 (December 30, 2016): 385–391. Accessed April 25, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/2024.