JENSEN, Anton. On the Homotopy Structure of Coverings. Mathematica Scandinavica, Berkeley, CA, United States, v. 6, p. 137–159, 1958. DOI: 10.7146/math.scand.a-10539. Disponível em: https://journals.msp.org/mscand/article/view/2806. Acesso em: 8 sep. 2026.