CHOI, Man-duen; ELLIOT, George A. Density of the self-adjoint elements with finite spectrum in an irrational rotation $C^*$-algebra. Mathematica Scandinavica, Berkeley, CA, United States, v. 67, p. 73–86, 1990. DOI: 10.7146/math.scand.a-12321. Disponível em: https://journals.msp.org/mscand/article/view/1355. Acesso em: 25 jul. 2026.