1. Reza AMERI, School of Mathematics, Statistics and Computer Science, College of Sciences, University of Tehran, P.O. Box 14155-6455, Teheran , Iran
2. School of Mathematics, Statistics and Computer Science, College of Sciences, University of Tehran, P.O. Box 14155-6455, Teheran , Iran
3. Department of Mathematics and Physics, University of Defence, Brno Kounicova 65, 662 10 Brno , Czech Republic