Institute of Informatics, University of Warsaw, Banacha 2, 02-097 Warsaw, Poland. piotr.dittwald@mimuw.edu.pl|Institute of Informatics, University of Warsaw, Banacha 2, 02-097 Warsaw, Poland. piotr.dittwald@mimuw.edu.pl|Institute of Informatics, University of Warsaw, Banacha 2, 02-097 Warsaw, Poland. piotr.dittwald@mimuw.edu.pl|Institute of Informatics, University of Warsaw, Banacha 2, 02-097 Warsaw, Poland. piotr.dittwald@mimuw.edu.pl