RomanyukA. S., SamoilenkoA. M., SerdyukA. S., and SokolenkoI. V. “International Conference "Theory of Approximation of Functions and Its applications" Dedicated to the 70 Th Birthday of the Corresponding Member of NASU Professor O. I. Stepanets (1942 - 2007)”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, no. 10, Oct. 2012, pp. 1438-40, https://umj.imath.kiev.ua/index.php/umj/article/view/2671.