1. 1 Sapientia Hungarian University of Transylvania , Cluj-Napoca , Romania , Dept. of Mathematics and Informatics
2. 2 Sapientia Hungarian University of Transylvania , Cluj-Napoca , Romania , Dept. of Mathematics and Informatics
3. 3 Babeş–Bolyai University , Cluj-Napoca , Romania , Faculty of Mathematics and Informatics