Dana 08.06.2015. (ponedjeljak) u 16 sati u predavaoni 109 u okviru Seminara za 

         unitarne reprezentacije i automorfne forme

of locally symmetric spaces to fix some notations, then we explain a
method to study the existence of ghost classes in the case of a Shimura
variety of Q-rank 2, where the complex structure allows us to use the
theory of Hodge structures. Finally we apply these strategies to the
Shimura varieties associated to GSp_4 and GU(2, 2).