Ideal class groups and subgroups of real quadratic function fields
  Here we study algebraic function fields K, give necessary and sufficient condition for the ideal class group $H(K)$ of any real quadratic function field $K$ to have a cyclic subgroup of order $n$, and obtain eight series of such fields $K$, with four of them NOT ERD-type or GERD-type. 
KunPeng Wang, Xianke Zhang