ROMANYUK, A. S.; ROMANYUK, V. S. Best bilinear approximations of functions from Nikolskii-Besov classes. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 64, n. 5, p. 685–697, 2012. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2608. Acesso em: 5 dec. 2025.