HILGERT, J.; HOFMANN, K. H. On the casual structure of homogeneous manifolds. MATHEMATICA SCANDINAVICA, [S. l.], v. 67, p. 119–144, 1990. DOI: 10.7146/math.scand.a-12324. Disponível em: https://www.mscand.dk/article/view/12324. Acesso em: 3 may. 2024.