KUMJIAN, Alexander. Preliminary algebras arising from local homeomorphisms. Mathematica Scandinavica, Berkeley, CA, United States, v. 52, p. 269–278, 1983. DOI: 10.7146/math.scand.a-12006. Disponível em: https://journals.msp.org/mscand/article/view/1616. Acesso em: 25 jul. 2026.