一类分式线性变换群的有限子群

Finite subgroups of some fractional linear transformations groups

证明PGL(2,Q)中仅有17个系数形如m+n p的分式线性变换有限子群并且决定了它们的构造,其中m,n是整数,p是素数.

Prove that there are only seventeen finite groups （the group operation is composition）of fractioal linear transformations with coefficients of the form m＋n√p,where m,n are both integers and p is prime.