GIFFEN, Charles H. Link concordance implies link homotopy. MATHEMATICA SCANDINAVICA, [S. l.], v. 45, p. 243–254, 1979. DOI: 10.7146/math.scand.a-11839. Disponível em: https://tidsskrift.dk/math/article/view/11839. Acesso em: 13 aug. 2026.