ROMANYUK, A. S.; ROMANYUK, V. S. Best Bilinear Approximations for the Classes of Functions of Many Variables. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 65, n. 12, p. 1681–1699, 2013. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2546. Acesso em: 6 dec. 2025.