POPOV, P. A. An Analog of the Jackson Inequality for Coconvex Approximation of Periodic Functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 53, n. 7, p. 919–928, 2001. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4313. Acesso em: 7 apr. 2025.