HANSEN, Vagn Lundsgaard. The characteristic algebra of a polynomial covering map. Mathematica Scandinavica, Berkeley, CA, United States, v. 64, p. 219–225, 1989. DOI: 10.7146/math.scand.a-12254. Disponível em: https://journals.msp.org/mscand/article/view/1397. Acesso em: 25 jul. 2026.