ROMANYUK, A.S. The best trigonometric and bilinear approximations of the functions of many variables from the classes $B_{p,\theta}^r$. I . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 44, n. 11, p. 1535–1547, 1992. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8257. Acesso em: 5 dec. 2025.