Lasuriya, R. A. “Multiple Fourier Sums on Sets of $\bar \psi$ -Differentiable Functions (Low Smoothness)”. Ukrains’kyi Matematychnyi Zhurnal 55, no. 7 (July 25, 2003): 911-918. Accessed May 21, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3966.