Document Type : Research Paper
1 School of Mathematics and Computer Sciences, Damghan University, P.O.Box 36715-364, Damghan, Iran.
2 Department of Mathematics and Computer Science, Damghan University, Iran.
3 school of mathematics and computer science, Damghan university
4 Department of Computer Sciences, Shahid Beheshti University, G.C. Tehran, Iran.
5 Department of Computer Sciences, University of Tabriz, Tabriz, Iran.