BLACKADAR, B. Shape theory for $C^*$-algebras. MATHEMATICA SCANDINAVICA, [S. l.], v. 56, p. 249–275, 1985. DOI: 10.7146/math.scand.a-12100. Disponível em: https://www.mscand.dk/article/view/12100. Acesso em: 17 jan. 2022.