Affiliations: Vinai K. Singh, Deparment of Mathematics, Inderprastha Engineering College, 63 Site IV, Surya Nagar Flyover Road, Sahibabad, Ghaziabad UP-201010 India, drvinaiksingh@ipec.org.in; Qin Sheng, Department of Mathematics, Baylor University, Waco, Texas 76706, USA, e-mail: qin_sheng@baylor.edu