FUGLEDE, B. On the Relation $PQ -QP = -iI$. Mathematica Scandinavica, Berkeley, CA, United States, v. 20, p. 79–88, 1967. DOI: 10.7146/math.scand.a-10822. Disponível em: https://journals.msp.org/mscand/article/view/2504. Acesso em: 25 jul. 2026.