BLACKADAR, Bruce. Shape theory for $C^*$-algebras. Mathematica Scandinavica, Berkeley, CA, United States, v. 56, p. 249–275, 1985. DOI: 10.7146/math.scand.a-12100. Disponível em: https://journals.msp.org/mscand/article/view/1526. Acesso em: 25 jul. 2026.