G. Tephnadze, “Strong Convergence of Two-Dimensional Walsh–Fourier Series”, Ukr. Mat. Zhurn., vol. 65, no. 6, pp. 822–834, Jun. 2013, Accessed: Feb. 16, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2467