AKEMANN, Charles A.; PEDERSEN, Gert K. Ideal perturbations of elements in $C^*$-Algebras. Mathematica Scandinavica, Berkeley, CA, United States, v. 41, p. 117–139, 1977. DOI: 10.7146/math.scand.a-11707. Disponível em: https://journals.msp.org/mscand/article/view/1937. Acesso em: 25 jul. 2026.