VRANCEANU, G. Variétés différentiables sans torsion. Mathematica Scandinavica, Berkeley, CA, United States, v. 21, p. 190–194, 1967. DOI: 10.7146/math.scand.a-10858. Disponível em: https://journals.msp.org/mscand/article/view/2469. Acesso em: 25 jul. 2026.