Department of Computer Science, University of Bielefeld, Bielefeld, Germany. schleif@informatik.uni-leipzig.de|Department of Computer Science, University of Bielefeld, Bielefeld, Germany. schleif@informatik.uni-leipzig.de|Department of Computer Science, University of Bielefeld, Bielefeld, Germany. schleif@informatik.uni-leipzig.de|Department of Computer Science, University of Bielefeld, Bielefeld, Germany. schleif@informatik.uni-leipzig.de|Department of Computer Science, University of Bielefeld, Bielefeld, Germany. schleif@informatik.uni-leipzig.de