PUTNAM, Ian F.; RORDAM, Mikael. The maximum unitary rank of some $C^*$-algebras. Mathematica Scandinavica, Berkeley, CA, United States, v. 63, p. 297–304, 1988. DOI: 10.7146/math.scand.a-12242. Disponível em: https://journals.msp.org/mscand/article/view/1422. Acesso em: 24 jul. 2026.