Arithmetic Subgroups of

This chapter describes the basic functionality for finite index subgroups of the modular group .

• Arithmetic subgroups (finite index subgroups of )
• Arithmetic subgroups defined by permutations
• Elements of Arithmetic Subgroups
• Congruence arithmetic subgroups of
• Congruence Subgroup
• Congruence Subgroup
• Congruence Subgroup
• Congruence Subgroup
• The modular group