MENNICKE, Jens. A Remark on the Congruence Subgroup Problem. Mathematica Scandinavica, Berkeley, CA, United States, v. 86, n. 2, p. 206–222, 2000. DOI: 10.7146/math.scand.a-14289. Disponível em: https://journals.msp.org/mscand/article/view/916. Acesso em: 25 jul. 2026.