BUSHEV, D. M. Approximation of classes of periodic functions with small smoothness. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 52, n. 2, p. 183–196, 2000. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4407. Acesso em: 5 dec. 2025.