SERDYUK, A. S.; STEPANETS, O. I. Lower bounds for widths of classes of convolutions of periodic functions in the metrics of $C$ and $L$. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 47, n. 8, p. 1112–1121, 1995. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5507. Acesso em: 5 dec. 2025.