GOL'BERG, A. L. Quasiconformal mappings and radii of normal systems of neighborhoods. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 51, n. 11, p. 1566–1568, 1999. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4758. Acesso em: 5 dec. 2025.