RUKASOV, V. I.; CHAICHENKO, S. O. Approximation of $\overline \psi$-Integrals of Periodic Functions by de la Vallée-Poussin Sums (Low Smoothness). Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 53, n. 12, p. 1641–1653, 2001. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4384. Acesso em: 5 dec. 2025.