1. Institut Préparatoire aux Etudes d'ingénieurs de Kairouan, Kairouan University, Kairouan, Tunisia
2. LR11ES53, FSS, Sfax University, Sfax, Tunisia
3. Faculty of Education, University of Ljubljana, Ljubljana, Slovenia
4. Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
5. Institute of Mathematics, Physics and Mechanics, Ljubljana, Slovenia