LANGARSHOEV, M. R. Sharp inequality of Jackson–Stechkin type and widths of functional classes in the space \( L_2 \). Eurasian Mathematical Journal, [S. l.], v. 5, n. 1, p. 122–134, 2014. Disponível em: https://emj.enu.kz/index.php/main/article/view/565. Acesso em: 26 aug. 2025.