KONONOVYCH, T. O. Lower bound for the best approximations of periodic summable functions of two variables and their conjugates in terms of Fourier coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 60, n. 8, p. 1042–1050, 2008. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3222. Acesso em: 5 dec. 2025.