DIGERNES, Trond. On Classes of Projections in a von Neumann Algebra. Mathematica Scandinavica, Berkeley, CA, United States, v. 31, p. 191–200, 1972. DOI: 10.7146/math.scand.a-11424. Disponível em: https://journals.msp.org/mscand/article/view/2222. Acesso em: 25 jul. 2026.