Institute of Computing Science, Poznaxc5x84 University of Technology, Poland. blazewic@sol.put.poznan.pl|Institute of Computing Science, Poznaxc5x84 University of Technology, Poland. blazewic@sol.put.poznan.pl|Institute of Computing Science, Poznaxc5x84 University of Technology, Poland. blazewic@sol.put.poznan.pl|Institute of Computing Science, Poznaxc5x84 University of Technology, Poland. blazewic@sol.put.poznan.pl|Institute of Computing Science, Poznaxc5x84 University of Technology, Poland. blazewic@sol.put.poznan.pl