ROMANYUK, A. S. Trigonometric widths of the classes $B_{p,θ}^ r$ of functions of many variables in the space $L_q$. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 50, n. 8, p. 1089–1097, 1998. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4858. Acesso em: 5 dec. 2025.