GARDNER, L. Terrell. Positivemaps of $C^*$-algebras commuting with a real continous function. Mathematica Scandinavica, Berkeley, CA, United States, v. 44, p. 196–200, 1979. DOI: 10.7146/math.scand.a-11802. Disponível em: https://journals.msp.org/mscand/article/view/1845. Acesso em: 25 jul. 2026.