DORONIN, V. G.; LIGUN, A. A. Exact constant in the Jackson inequality in the space L2. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 9, p. 1261–1265, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5643. Acesso em: 5 dec. 2025.