SHVAI, K. V. Estimates of the best bilinear approximations for the classes of $(ψ,β)$-differentiable periodic multivariate functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 70, n. 4, p. 564–573, 2018. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1576. Acesso em: 14 apr. 2025.