K. V. Solich, “Best bilinear approximations of the classes $S^{\Omega}_{p, \theta}B$ of periodic functions of many variables”, Ukr. Mat. Zhurn., vol. 63, no. 6, pp. 809–826, Jun. 2011, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2764