HILGERT, Joachim; HOFMANN, Karl H. On the casual structure of homogeneous manifolds. Mathematica Scandinavica, Berkeley, CA, United States, v. 67, p. 119–144, 1990. DOI: 10.7146/math.scand.a-12324. Disponível em: https://journals.msp.org/mscand/article/view/1354. Acesso em: 25 jul. 2026.