1. Department of Mathematics and Informatics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovica 4, 21000 Novi Sad, Serbia. kurba@dmi.uns.ac.rs, mira@dmi.uns.ac.rs
2. Institute of Psychology, Humboldt University Berlin, Rudower Chaussee 18, 12489 Berlin, Germany. charlotte.bernstorff@hu-berlin.de, jens.nachtwei@hu-berlin.de
3. Institute of Informatics, Humboldt University Berlin, Rudower Chaussee 25, 12489 Berlin, Germany. hdb@informatik.hu-berlin.de