Institute of Computing Science, Poznan University of Technology, Piotrowo 2, Poznan, 60-965, Poland. maciej.antczak@cs.put.poznan.pl.|Institute of Computing Science, Poznan University of Technology, Piotrowo 2, Poznan, 60-965, Poland.|Institute of Computing Science, Poznan University of Technology, Piotrowo 2, Poznan, 60-965, Poland.|Institute of Computing Science, Poznan University of Technology, Piotrowo 2, Poznan, 60-965, Poland.