Shydlich, A. L. “Saturation of the Linear Methods of Summation of Fourier Series in the Spaces <i>S<sup> p</sup></i><sub>φ</Sub&gt;”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, no. 6, June 2008, pp. 815 -, https://umj.imath.kiev.ua/index.php/umj/article/view/3198.