Kaur, Kulwinder, S. S. Bhatia, and Babu Ram. “Double Trigonometric Series With Coefficients of Bounded Variation of Higher Order”. Tamkang Journal of Mathematics 35, no. 3 (September 30, 2004): 267–280. Accessed April 16, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/208.