PETRENKO, O. V.; PROTASOV, I. V. Balleans and G -spaces. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 64, n. 3, p. 344–350, 2012. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2580. Acesso em: 5 dec. 2025.