ZELENYUK, E. G. Topologically free subsets of universal algebras. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 5, p. 651–661, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5045. Acesso em: 5 dec. 2025.