Congruence subgroups of SL(2,Integers)

Version 1.2.5
Released 2023-02-25

This project is maintained by Ann Dooms, Olexandr Konovalov, Helena Verrill

GAP Package Congruence

The Congruence package provides functions to construct several types of canonical congruence subgroups in SL_2(Z), and also intersections of a finite number of such subgroups. Furthermore, it implements the algorithm for generating Farey symbols for congruence subgroups and using them to produce a system of independent generators for these subgroups

The current version of this package is version 1.2.5, released on 2023-02-25. For more information, please refer to the package manual. There is also a README file.


This package requires GAP version >=4.8

The following other GAP packages are needed:


Ann Dooms, Eric Jespers, Olexandr Konovalov, Helena Verrill.


For bug reports, feature requests and suggestions, please use the issue tracker.