JONES, Gareth A. Counting subgroups of non-euclidean crystallographic groups. MATHEMATICA SCANDINAVICA, [S. l.], v. 84, n. 1, p. 23–39, 1999. DOI: 10.7146/math.scand.a-13930. Disponível em: https://tidsskrift.dk/math/article/view/13930. Acesso em: 14 aug. 2026.