1. Department of Mathematics, College of Science, Princess Nourah Bint Abdulrahman University, Riyadh, Saudi Arabia
2. Department of Basic Sciences, University of Engineering and Technology, Peshawar, Khyber Pakhtunkhwa, Pakistan
3. Section of Mathematics, International Telematic University Uninettuno, Corso Vittorio Emanuele II, 39, 00186 Roma, Italy