FUGLEDE, B. On the Relation $PQ -QP = -iI$. MATHEMATICA SCANDINAVICA, [S. l.], v. 20, p. 79–88, 1967. DOI: 10.7146/math.scand.a-10822. Disponível em: https://tidsskrift.dk/math/article/view/10822. Acesso em: 14 aug. 2026.