SARREITHER, Paul. Zur algebraischen Vielfachheit eines Produktes von Operatorscharen. Mathematica Scandinavica, Berkeley, CA, United States, v. 41, p. 185–192, 1977. DOI: 10.7146/math.scand.a-11712. Disponível em: https://journals.msp.org/mscand/article/view/1933. Acesso em: 25 jul. 2026.