DEREV’YANKO, N. V. Trigonometric widths of classes of periodic functions of many variables. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 64, n. 8, p. 1041–1052, 2012. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2639. Acesso em: 6 dec. 2025.