SHYDLICH, A. L. Order equalities for some functionals and their application to the estimation of the best $n$-term approximations and widths. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 61, n. 10, p. 1403–1423, 2009. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3110. Acesso em: 14 apr. 2025.