The set of linear Möbius transformations which satisfy
where and are odd and and are even. is a subgroup of the modular group Gamma, and is also called the theta subgroup. The fundamental region of the modular lambda group is illustrated above.
The set of linear Möbius transformations which satisfy
where and are odd and and are even. is a subgroup of the modular group Gamma, and is also called the theta subgroup. The fundamental region of the modular lambda group is illustrated above.
Weisstein, Eric W. "Modular Group Lambda." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ModularGroupLambda.html