VOITENKO, S. P. Best orthogonal trigonometric approximations of the classes $B^{Ω}_{p,θ}$ of periodic functions of many variables. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 61, n. 11, p. 1473–1484, 2009. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3115. Acesso em: 27 apr. 2025.