Identifying congruence subgroups of the modular group
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- Proc. Amer. Math. Soc. 124 (1996), 1351-1359 Request permission
Abstract:
We exhibit a simple test (Theorem 2.4) for determining if a given (classical) modular subgroup is a congruence subgroup, and give a detailed description of its implementation (Theorem 3.1). In an appendix, we also describe a more โinvariantโ and arithmetic congruence test.References
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Additional Information
- Tim Hsu
- Affiliation: Department of Mathematics, Princeton University, Princeton, New Jersey 08544
- Address at time of publication: Department of Mathematics, University of Michigan, Ann Arbor, Michigan 48109
- Email: timhsu@math.princeton.edu, timhsu@math.lsa.umich.edu
- Received by editor(s): September 1, 1994
- Additional Notes: The author was supported by an NSF graduate fellowship and DOE GAANN grant #P200A10022.A03.
- Communicated by: Ronald M. Solomon
- © Copyright 1996 American Mathematical Society
- Journal: Proc. Amer. Math. Soc. 124 (1996), 1351-1359
- MSC (1991): Primary 20H05; Secondary 20F05
- DOI: https://doi.org/10.1090/S0002-9939-96-03496-X
- MathSciNet review: 1343700