Vakarchuk, S., V. Zabutna, and M. Vakarchuk. “Averaged Characteristics of Smoothness in $L_2$ and Estimations for the Widths Values of Function Classes”. Ukrains’kyi Matematychnyi Zhurnal 77, no. 2 (April 3, 2025): 83–106. Accessed April 7, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8794.