JENSEN, A. On the Homotopy Structure of Coverings. MATHEMATICA SCANDINAVICA, [S. l.], v. 6, p. 137–159, 1958. DOI: 10.7146/math.scand.a-10539. Disponível em: https://www.mscand.dk/article/view/10539. Acesso em: 2 may. 2024.