1. Department of Mathematics and Computer Sciences, Necmettin Erbakan University, Konya 42090, Turkey
2. Department of Mathematics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
3. Section of Mathematics, International Telematic University Uninettuno, Corso Vittorio Emanuele II, 3900186 Roma, Italy
4. Department of Mathematics, Faculty of Science, Khon Kaen University, Khon Kaen, 40002 Thailand