Fedunyk-Yaremchuk, O.V., and S.B. Hembars'ka. “Best Orthogonal Trigonometric Approximations of the Nikol’skii-Besov-Type Classes of Periodic Functions of One and Several Variables”. Carpathian Mathematical Publications 14, no. 1 (June 22, 2022): 171–184. Accessed November 24, 2024. https://journals.pnu.edu.ua/index.php/cmp/article/view/5928.