1. Department of Mathematics, Fatih University, 34900 Büyükçekmece, Istanbul, Turkey
2. Department of Applied Mathematics, International Turkmen-Turkish University, 32 Gerogly Street, Ashgabat 74400, Turkmenistan
3. Department of Mathematics, Yildiz Technical University, Davutpasa Campus, 34210 Esenler, Istanbul, Turkey
4. Institute of Mathematics, Hebrew University, Givat Ram, Jerusalem 91904, Israel