HOLE, Arne. Invariant Differential Operators and Polynomials of Lie Transformation Groups. Mathematica Scandinavica, Berkeley, CA, United States, v. 34, p. 109–123, 1974. DOI: 10.7146/math.scand.a-11511. Disponível em: https://journals.msp.org/mscand/article/view/2136. Acesso em: 25 jul. 2026.