The Hilbert modular group and orthogonal groups

Adrian Hauffe-Waschbüsch, Aloys Krieg
2022 Research in number theory 8(3)  
We derive an explicit isomorphism between the Hilbert modular group and certain congruence subgroups on the one hand and particular subgroups of the special orthogonal group SO(2, 2) on the other hand. The proof is based on an application of linear algebra adapted to number theoretical needs.
doi:10.18154/rwth-2022-06975 fatcat:fzp7rul6bbbfhobx5a2oadku5u