MAAK, Wilhelm. Periodizitätseigenschaften unitäter Gruppen in Hilberträumen. Mathematica Scandinavica, Berkeley, CA, United States, v. 2, p. 333–343, 1954. DOI: 10.7146/math.scand.a-10419. Disponível em: https://journals.msp.org/mscand/article/view/2905. Acesso em: 25 jul. 2026.