DOERAENE , Jean-Paul; EL HAOUARI , Mohammed. Yet another Hopf invariant. North-Western European Journal of Mathematics, [S. l.], n. 4, p. 185–197, 2018. Disponível em: https://nwejm.univ-lille.fr/index.php/nwejm/article/view/49.. Acesso em: 18 oct. 2024.