LÖFWALL, Clas. Appendix to "On the double Poincaré series of the enveloping algebras of certain graded Lie algebras". Mathematica Scandinavica, Berkeley, CA, United States, v. 51, p. 59–62, 1982. DOI: 10.7146/math.scand.a-11964. Disponível em: https://journals.msp.org/mscand/article/view/1685. Acesso em: 25 jul. 2026.