DOVGHEY, Zh.; SUMARYUK, M. Free subsemigroups in automorphism group of a polynomial ring of two variables over number fields. Carpathian Mathematical Publications, [S. l.], v. 3, n. 2, p. 64–70, 2011. Disponível em: https://personnel.pnu.edu.ua/index.php/cmp/article/view/3066. Acesso em: 19 jan. 2025.