Kononovych, T.O. (2004) “Estimate for the Best Approximation of Summable Functions of Two Variables in Terms of Fourier Coefficients”,
Ukrains’kyi Matematychnyi Zhurnal, 56(1), pp. 51–69. Available at:
https://umj.imath.kiev.ua/index.php/umj/article/view/3727 (Accessed: 7 April 2025).