FRÖBERG, R. A study of graded extremal rings and of monominal rings. MATHEMATICA SCANDINAVICA, [S. l.], v. 51, p. 22–34, 1982. DOI: 10.7146/math.scand.a-11961. Disponível em: https://www.mscand.dk/article/view/11961. Acesso em: 28 apr. 2024.