K. V. Solich, “Estimates for bilinear approximations of the classes TeX of periodic functions of two variables”, Ukr. Mat. Zhurn., vol. 64, no. 8, pp. 1106–1120, Aug. 2012, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2644