StasyukS. A. “Kolmogorov Widths for Analogs of the Nikol’skii–Besov Classes With Logarithmic Smoothness”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 67, no. 11, Nov. 2015, pp. 1579-84, https://umj.imath.kiev.ua/index.php/umj/article/view/2092.