DIMITROVA, I.; KOPPITZ, J. On relative ranks of finite transformation semigroups with restricted range. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 73, n. 5, p. 617–626, 2021. DOI: 10.37863/umzh.v73i5.288. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/288. Acesso em: 5 dec. 2025.