RomanyukA. S., and RomanyukV. S. “Best Bilinear Approximations of Functions from Nikolskii-Besov Classes”. Ukrains’kyi Matematychnyi Zhurnal 64, no. 5 (May 25, 2012): 685-697. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2608.