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P. Malakooti Rad
Department of Mathematics, Islamic Azad University, Qazvin Branch, Qazvin, Iran.
S. Yassemi
School of Mathematics, Statistics and Computer Science, College of Science, University of Tehran, Tehran, Iran, and School of Mathematics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5746, Tehran, Iran.
Sh. Ghalandarzadeh
Department of Mathematics, Faculty of Science, K. N. Toosi University of Technology, Tehran, Iran.
P. Safari
Department of Mathematics, Islamic Azad University, Qazvin Branch, Qazvin, Iran.