Romanyuk, A. S. (2006). Best approximations of the classes $B_{p,\,\theta}^{r}$ of periodic functions of many variables in uniform metric.
Ukrains’kyi Matematychnyi Zhurnal,
58(10), 1395–1406.
https://umj.imath.kiev.ua/index.php/umj/article/view/3541