BUSHEV, D. M.; KOVAL'CHUK, I. R. On approximation of convolution classes. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 1, p. 26–31, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5778. Acesso em: 14 apr. 2025.