LAURSEN, K. B.; SINCLAIR, A. M. Lifting matrix units in $C^*$-algebras II. MATHEMATICA SCANDINAVICA, [S. l.], v. 37, p. 167–172, 1975. DOI: 10.7146/math.scand.a-11598. Disponível em: https://www.mscand.dk/article/view/11598. Acesso em: 8 may. 2024.