HALPERN, Herbert. Spectra of operator equations and automorphism groups of von Neumann algebras. Mathematica Scandinavica, Berkeley, CA, United States, v. 42, p. 135–149, 1978. DOI: 10.7146/math.scand.a-11742. Disponível em: https://journals.msp.org/mscand/article/view/1906. Acesso em: 25 jul. 2026.