PRESTIN, J.; SAVCHUK, V. V.; SHYDLICH, A. L. Direct and inverse theorems on the approximation of 2π -periodic functions by Taylor – Abel – Poisson operators. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 69, n. 5, p. 657, 2017. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1725. Acesso em: 5 dec. 2025.