Simplicity of twin tree lattices with non-trivial commutation relations
  We prove a simplicity criterion for certain twin tree lattices. It applies to all rank two Kac-Moody groups over finite fields with non-trivial commutation relations, thereby yielding examples of simple non-uniform lattices in the product of two trees. 
Pierre-Emmanuel Caprace, Bertrand Remy (ICJ)
math.GR