Romanyuk, A. S., et al. “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.