PORTER, Tim. Borsuk’s Theory of Shape and Cech Homotopy. MATHEMATICA SCANDINAVICA, [S. l.], v. 33, p. 83–89, 1973. DOI: 10.7146/math.scand.a-11473. Disponível em: https://tidsskrift.dk/math/article/view/11473. Acesso em: 14 aug. 2026.