KOSCHORKE, Ulrich; SANDERSON, Brian. Geometric interpretations of the generalized Hopf invariant. Mathematica Scandinavica, Berkeley, CA, United States, v. 41, p. 199–217, 1977. DOI: 10.7146/math.scand.a-11714. Disponível em: https://journals.msp.org/mscand/article/view/1931. Acesso em: 25 jul. 2026.