Modular Group Gamma_0

Let  be a positive integer, then  is defined as the set of all matrices  in the modular group Gamma  with .  is a subgroup of . For any prime , the set

is a fundamental region of the subgroup , where  and  (Apostol 1997).

REFERENCES:

Apostol, T. M. "The Subgroup " and "Fundamental Region ." §4.2-4.3 in Modular Functions and Dirichlet Series in Number Theory, 2nd ed. New York: Springer-Verlag, pp. 75-78, 1997.