MASKIT, Bernard. A remark on degenerate groups. Mathematica Scandinavica, Berkeley, CA, United States, v. 36, p. 17–20, 1975. DOI: 10.7146/math.scand.a-11558. Disponível em: https://journals.msp.org/mscand/article/view/2060. Acesso em: 25 jul. 2026.