PORTER, Tim. Borsuk’s Theory of Shape and Cech Homotopy. Mathematica Scandinavica, Berkeley, CA, United States, v. 33, p. 83–89, 1973. DOI: 10.7146/math.scand.a-11473. Disponível em: https://journals.msp.org/mscand/article/view/2196. Acesso em: 25 jul. 2026.