ORLIK, Peter. Homotopy 4-Spheres Have Little Symmetry. Mathematica Scandinavica, Berkeley, CA, United States, v. 33, p. 275–278, 1973. DOI: 10.7146/math.scand.a-11490. Disponível em: https://journals.msp.org/mscand/article/view/2176. Acesso em: 25 jul. 2026.