例句與造句

1. An interesting example is the modular group G = \ mathrm { SL } _ 2 ( \ mathbb Z ) : it acts on the tree given by the 1-skeleton of the associated tessellation of the hyperbolic plane and it has a finite index free subgroup ( on two generators ) of index 6 ( for example the set of matrices in G which reduce to the identity modulo 2 is such a group ).
2. It's difficult to find modular group g in a sentence. 用modular group g造句挺難的