AKEMANN, C. A.; PEDERSEN, G. K. Ideal perturbations of elements in $C^*$-Algebras. MATHEMATICA SCANDINAVICA, [S. l.], v. 41, p. 117–139, 1977. DOI: 10.7146/math.scand.a-11707. Disponível em: https://www.mscand.dk/article/view/11707. Acesso em: 4 may. 2024.