MOLDAVANSKY, D. I. Finite approximation of descending HNN-expansions of groups. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 44, n. 6, p. 842–845, 1992. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8020. Acesso em: 5 dec. 2025.