to the moduli space of the torus, is any fundamental domain for the modulargroup P S L ( 2 , Z ) {\displaystyle PSL(2,\mathbb {Z} )} acting on the upper
{\displaystyle q=e^{2\pi i\tau }} 是nome(英语:nome (mathematics))的平方。 上述二個函數都有模群(英语:modulargroup)下的對稱性。 歐拉函數(也稱為歐拉商數) Apostol, Tom M., Introduction to analytic number