BUSHEV, D. M.; KHARKEVYCH, Yu. I. Approximation of classes of periodic multivariable functions by linear positive operators. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 58, n. 1, p. 12–19, 2006. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3430. Acesso em: 5 dec. 2025.