KORNEICHUK, N. P. On the best approximation of functions of $n$ variables. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 51, n. 10, p. 1352–1359, 1999. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4734. Acesso em: 5 dec. 2025.