1. Faculty of Computer Science, Polish-Japanese Academy of Information Technology, Warsaw, Poland. asawicka@pja.edu.pl
2. Faculty of Computer Science, Bialystok University of Technology, Bialystok, Poland. m.kacprzak@pb.edu.pl
3. Faculty of Mathematics and Natural Sciences, Jan Długosz University, Czestochowa, Poland. a.zbrzezny@ujd.edu.pl