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# GAP package Congruence
The GAP package Congruence 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.
Congruence does not use external binaries and, therefore, works without
restrictions on the type of the operating system. It is redistributed with
GAP, but is not loaded by default. Therefore, to use Congruence, first you
need to load it using the following command:
gap> LoadPackage("congruence");
Ann Dooms, Eric Jespers, Olexandr Konovalov, Helena Verrill
