1. Institute of Informatics, Białystok University, Sosnowa 64, 15-887 Białystok, Poland. anna.gom@math.uwb.edu.pl
2. Department of Logic and Methodology of Science, Maria Curie-Skłodowska University, pl. Maria Curie-Skłodowska 4, 20-031 Lublin, Poland. marcin.wolski@umcs.lublin.pl