KOSCHORKE, U.; SANDERSON, B. Geometric interpretations of the generalized Hopf invariant. MATHEMATICA SCANDINAVICA, [S. l.], v. 41, p. 199–217, 1977. DOI: 10.7146/math.scand.a-11714. Disponível em: https://www.mscand.dk/article/view/11714. Acesso em: 5 may. 2024.