Kao, Chung-Siung. “On Errors of a Unified Family of Approximation Forms of Bivariate Continuous Functions”. Tamkang Journal of Mathematics 34, no. 4 (December 31, 2003): 371–382. Accessed April 29, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/239.