Löfwall, Clas. “Appendix to ‘On the Double Poincaré Series of the Enveloping Algebras of Certain Graded Lie algebras’”. Mathematica Scandinavica 51 (June 1, 1982): 59–62. Accessed July 25, 2026. https://journals.msp.org/mscand/article/view/1685.