STEPANETS, O. I. Inverse theorems on approximation of periodic functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 47, n. 9, p. 1266–1273, 1995. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5527. Acesso em: 11 apr. 2025.