Stepanets , A. I. “ Certain Remarks on Approximation of the Hing Smoothness Functions by the Fourier Operators”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 1 (February 4, 1992): 138–141. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/7806.