PICHUGOV, S. A. On the Jackson theorem for periodic functions in metric spaces with integral metric. II. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 63, n. 11, p. 1524–1533, 2011. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2822. Acesso em: 5 dec. 2025.