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
This package requires GAP version >=4.8
The following other GAP packages are needed:
For bug reports, feature requests and suggestions, please use the issue tracker.