Mikołajewski, Dariusz, Institute of Mechanics and Applied Computer Science, Kazimierz Wielki University,ul. Koperni- ka 1, 85-074 Bydgoszcz, Poland, and Department of Informatics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, ul. Grudziadzka 5, 87-100, Torun, Poland, Poland