VOLCHKOV, V. V. On exact constants in Jackson-type inequalities in the space $L^2$. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 47, n. 1, p. 108–110, 1995. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5388. Acesso em: 14 apr. 2025.