PICHUGOV, S. A. Multiple modules of continuity and the best approximations of periodic functions in metric spaces. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 70, n. 5, p. 699–707, 2018. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1588. Acesso em: 5 dec. 2025.