1. 1Faculty of Economics and Administrative Sciences, Department of International Trade, Cankiri Karatekin University, Cankiri, Turkey
2. 2Art-Science Faculty, Department of Mathematics and Computer Science, Eskisehir Osmangazi University, Eskisehir, Turkey, E-mail: ssan@ogu.edu.tr (S. San)
3. 3Art-Science Faculty, Department of Mathematics and Computer Science, Eskisehir Osmangazi University, Eskisehir, Turkey, E-mail: abekir@ogu.edu.tr (A. Bekir)
4. 4Faculty of Arts and Sciences, Department of Mathematics, Uludag University, Bursa, Turkey, E-mail: eyasar@uludag.edu.tr