SERDYUK, A. S. Widths and best approximations for classes of convolutions of periodic functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 51, n. 5, p. 674–687, 1999. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4653. Acesso em: 6 dec. 2025.