GARDNER, L. T. Positivemaps of $C^*$-algebras commuting with a real continous function. MATHEMATICA SCANDINAVICA, [S. l.], v. 44, p. 196–200, 1979. DOI: 10.7146/math.scand.a-11802. Disponível em: https://www.mscand.dk/article/view/11802. Acesso em: 5 may. 2024.