ROMANYUK, A. S. Trigonometric and linear widths for the classes of periodic multivariable functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 69, n. 5, p. 670–681, 2017. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1726. Acesso em: 5 dec. 2025.