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