SavchukV. V. “Best Linear Methods of Approximation and Optimal Orthonormal Systems of the Hardy Space”. Ukrains’kyi Matematychnyi Zhurnal 60, no. 5 (May 25, 2008): 636–646. Accessed November 23, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3182.