SAVCHUK, V. V. Best linear methods of approximation and optimal orthonormal systems of the Hardy space. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 60, n. 5, p. 636–646, 2008. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3182. Acesso em: 6 dec. 2025.