A. . Romanyuk, “The best trigonometric and bilinear approximations of the functions of many variables from the classes $B_{p,\theta}^r$. I ”, Ukr. Mat. Zhurn., vol. 44, no. 11, pp. 1535–1547, Nov. 1992, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/8257