Author(s):
1. Tomislav Pavlović, University of Nis, Faculty of Sciences and Mathematics, , Serbia
2. Dragoljub Mirjanić, Akademija nauka i umjetnosti Republike Srpske, Republic of Srpska, Bosnia and Herzegovina
3. Ivana Radonjić, University of Nis, Faculty of Sciences and Mathematics, , Serbia
4. Darko Divnić, Akademija nauka i umjetnosti Republike Srpske, Republic of Srpska, Bosnia and Herzegovina