Affiliation: | 1. Department of Mathematics, Zhejiang University, Hangzhou, 310027, China 2. Department of Mathematics, Islamic Azad University, Najafabad Branch, Najafabad, Iran 3. Department of Mathematics, Faculty of Science, Malayer University, Malayer, Iran 4. Department of Applied Mathematics, Faculty of mathematical Science, Shahrekord University, P. O. Box 115, Shahrekord, Iran
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