Author(s):
1. Danijela Ćetković, Faculty of Natural Sciences and Mathematics, University of Tuzla , Republic of Srpska, Bosnia and Herzegovina
2. Oleg Lesmajster, Prirodno-matematički fakultet Banja Luka, Republic of Srpska, Bosnia and Herzegovina
3. Dragan Vuković, Republic of Srpska, Bosnia and Herzegovina
4. Bojana Milinković, Prirodno-matematički fakultet Banja Luka, Republic of Srpska, Bosnia and Herzegovina