Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle, Germany. eggeling@cs.helsinki.fi.|Department of Computer Science, Helsinki Institute for Information Technology HIIT, University of Helsinki, Helsinki, Finland. teemu.roos@cs.helsinki.fi.|Department of Computer Science, Helsinki Institute for Information Technology HIIT, University of Helsinki, Helsinki, Finland. petri.myllymaki@cs.helsinki.fi.|Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle, Germany. grosse@informatik.uni-halle.de.