Institute of Computer Science, Polish Academy of Science, Ordona 21, PL-01-237 Warsaw, Poland.|Institute of Computer Science, Polish Academy of Science, Ordona 21, PL-01-237 Warsaw, Poland.|Institute of Computer Science, Polish Academy of Science, Ordona 21, PL-01-237 Warsaw, Poland.|Institute of Computer Science, Polish Academy of Science, Ordona 21, PL-01-237 Warsaw, Poland.|Institute of Computer Science, Polish Academy of Science, Ordona 21, PL-01-237 Warsaw, Poland.|Institute of Computer Science, Polish Academy of Science, Ordona 21, PL-01-237 Warsaw, Poland.