HEISTAD, E. Excision in Singular Theory. MATHEMATICA SCANDINAVICA, [S. l.], v. 20, p. 61–64, 1967. DOI: 10.7146/math.scand.a-10820. Disponível em: https://www.mscand.dk/article/view/10820. Acesso em: 3 may. 2024.