1. Faculty of Mathematics, University of Belgrade, Studentski trg 16, 11158 Belgrade, Serbia
2. Institute of Physics Belgrade, University of Belgrade, 11080 Belgrade, Serbia
3. Mathematical Institute of the Serbian Academy of Sciences and Arts, 11000 Belgrade, Serbia
4. Laboratory for Theoretical Cosmology, International Centre of Gravity and Cosmos, Tomsk State University of Control Systems and Radioelectronics (TUSUR), 634050 Tomsk, Russia
5. Faculty of Education, University of Belgrade, Kraljice Natalije 43, 11000 Belgrade, Serbia