HEISTAD, Egil. Excision in Singular Theory. Mathematica Scandinavica, Berkeley, CA, United States, v. 20, p. 61–64, 1967. DOI: 10.7146/math.scand.a-10820. Disponível em: https://journals.msp.org/mscand/article/view/2501. Acesso em: 25 jul. 2026.