VAKARCHUK, S. B.; SHCHITOV, A. N. Best Polynomial Approximations in $L_2$ and Widths of Some Classes of Functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 56, n. 11, p. 1458–1466, 2004. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3858. Acesso em: 27 apr. 2025.