STEPANETS, O. I. Problems of approximation theory in linear spaces. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 58, n. 1, p. 47–92, 2006. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3434. Acesso em: 5 dec. 2025.