FEDORENKO, An. S. Approximation of classes $C_\infty ^{\bar \psi }$ by zygmund sumsby zygmund sums. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 52, n. 6, p. 856–860, 2000. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4483. Acesso em: 27 apr. 2025.