Discreteness criterion for subgroups of products of SL(2)
Let G be a finite product of SL(2, K
)’s for local fields K
of characteristic zero. We present a discreteness criterion for nonsolvable subgroups of G containing an irreducible lattice of a maximal unipotent subgroup of G. In particular, such a subgroup has to be arithmetic. This extends a previous result of A. Selberg when G is a product of SL2()’s.