1. Department of Mathematics, YMCA University of Science and Technology, Faridabad (Haryana) 121 006, India
2. Department of Mathematics, Indira Gandhi National Tribal University, Lalpur, Amarkantak 484 887, Madhya Pradesh, India
3. L. 1627 Awadh Puri Colony, Beniganj, Phase III, Opposite Industrial Training Institute (I.T.I.), Ayodhya main road, Faizabad 224 001, Uttar Pradesh, India
4. Faculty of Applied Mathematics and Control Processes, St. Peterburg State University, Saint Petersburg, 198 504, Russia