Congruence subgroup
In mathematics Kongruenzuntergruppen are a class of discrete arithmetically defined subgroups of the general linear group.
Definition
Be
A via defined algebraic group, and is a natural number. Then
A congruence subgroup. ( Herein, the limitation of the " modulo N reduction .")
Arithmetic groups
Kongruenzuntergruppen are arithmetic ( by construction ) groups. For each arithmetic group contains a congruence subgroup.