KONONOVYCH, T. O. Estimate for the Best Approximation of Summable Functions of Two Variables in Terms of Fourier Coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 56, n. 1, p. 51–69, 2004. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3727. Acesso em: 7 apr. 2025.