RANDELL, Richard. Index invariants of orbit spaces. Mathematica Scandinavica, Berkeley, CA, United States, v. 36, p. 263–270, 1975. DOI: 10.7146/math.scand.a-11575. Disponível em: https://journals.msp.org/mscand/article/view/2042. Acesso em: 25 jul. 2026.