CUNTZ, Joachim. The structure of multiplication and addition in simple $C^*$-algebras. Mathematica Scandinavica, Berkeley, CA, United States, v. 40, p. 215–233, 1977. DOI: 10.7146/math.scand.a-11691. Disponível em: https://journals.msp.org/mscand/article/view/1956. Acesso em: 25 jul. 2026.