1. Department of Basic, Anhui Sanlian University, China
2. Department of Mathematics, University of Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan
3. Department of Computing, Mathematics and Electronics, "1 Decembrie 1918" University of Alba Iulia, Alba Iulia, 510 0 09, Romania
4. Faculty of Mathematics and Computer Science, Transilvania University of Brasov, Iuliu Maniu Street 50, 500091 Brasov, Romania