Document Type : Original Manuscript
Authors
1 Department of Mathematics, Hakim Sabzevari University, P. O. Box 96179-76487, Sabzevar, Iran
2 Department of Mathematics, Department of Mathematics, Ferdowsi University of Mashhad, P.O.Box 1159-91775, Mashhad, Iran.
3 Department of Mathematics, Center of Excellence in Analysis on Algebraic Struc- tures, Ferdowsi University of Mashhad, P.O.Box 1159-91775, Mashhad, Iran.
Abstract
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