FORELLI, Frank. Two-sheeted coverings of the disc. Mathematica Scandinavica, Berkeley, CA, United States, v. 61, p. 17–38, 1987. DOI: 10.7146/math.scand.a-12189. Disponível em: https://journals.msp.org/mscand/article/view/1482. Acesso em: 25 jul. 2026.