Congruence testing for odd subgroups of the modular group
Number Theory
2019-02-20 v1
Abstract
We give a computationally effective criterion for determining whether a finite-index subgroup of SL(2, Z) is a congruence subgroup, extending earlier work of Hsu for subgroups of PSL(2, Z).
Cite
@article{arxiv.1307.0625,
title = {Congruence testing for odd subgroups of the modular group},
author = {Thomas Hamilton and David Loeffler},
journal= {arXiv preprint arXiv:1307.0625},
year = {2019}
}