HANSEN, V. L. The characteristic algebra of a polynomial covering map. MATHEMATICA SCANDINAVICA, [S. l.], v. 64, p. 219–225, 1989. DOI: 10.7146/math.scand.a-12254. Disponível em: https://www.mscand.dk/article/view/12254. Acesso em: 3 may. 2024.