SHABAT, G.; SHABAT, V.; RAZIN, M. Edge operators. Mathematica Scandinavica, Berkeley, CA, United States, v. 81, p. 199–211, 1997. DOI: 10.7146/math.scand.a-12874. Disponível em: https://journals.msp.org/mscand/article/view/1031. Acesso em: 24 jul. 2026.