Modular symmetry at level 6 and a new route towards finite modular groups

Cai-Chang Li, Xiang-Gan Liu, Gui-Jun Ding

We propose to construct the finite modular groups from the quotient of two principal congruence subgroups as $\Gamma (N^{\prime })/\Gamma (N")$, and the modular group $SL(2,\mathbb{Z})$ is extended to…