FRÖBERG, Ralf. 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://tidsskrift.dk/math/article/view/11961. Acesso em: 14 aug. 2026.