Hecke Operators for Period Functions for Congruence Subgroups
  This is basically a summary of [Mu]. The focus of the paper is the explicit computation of Hecke operators for period functions. In particular we compute the matrix representations of the 2nd Hecke operator on period functions for the full modular group $SL(2,Z)$ and the congruence subgroup $\Gamma_0(2)$.   [Mu] Tobias M\"uhlenbruch. Hecke operators on period functions for $\Gamma_0(N)$. Journal of Number Theory. http://dx.doi.org/10.1016/j.jnt.2005.09.003 
Tobias M\"uhlenbruch