Affiliation: | 1. University of Central Florida, Department of Mathematics, 4000 Central Florida Blvd., P.O. Box 161364, Orlando, FL 32816-1364, USA;2. University of South Dakota, Department of Mathematical Sciences, 414 E. Clark St., Vermillion, SD 57069, USA;3. Department of Mathematics and Statistics, Southern Illinois University Edwardsville, Campus Box 1653, Science Building, Edwardsville, IL 62026, USA |