1. Department of Mechanics, Faculty of Technical Sciences, University of Novi Sad, Trg D. Obradovica 6, 21000 Novi Sad, Serbia
2. Mathematical Institute, Serbian Academy of Arts and Sciences, Kneza Mihaila 36, 11000 Belgrade, Serbia
3. Faculty of Education in Sombor, University of Novi Sad, Podgorička 4, 25000 Sombor, Serbia
4. Department of Mathematics, Faculty of Natural Sciences and Mathematics, University of Novi Sad, Trg D. Obradovica 4, 21000 Novi Sad, Serbia