Romanyuk, A. S. “Best Approximations of the Classes $B_{p,\,\theta}^{r}$ of Periodic Functions of Many Variables in Uniform Metric”. Ukrains’kyi Matematychnyi Zhurnal 58, no. 10 (October 25, 2006): 1395–1406. Accessed April 7, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3541.