Affiliation: | 1. Department of Mathematics, University of Alabama, Tuscaloosa, Alabama, USAmdixon@ua.edu mdixon@as.ua.edu;3. Department of Algebra, Facultet ofMathematic and Mechanik, National University of Dnepropetrovsk, Dnepropetrovsk, Ukraine;4. Department of Mathematics-IUMA, University of Zaragoza, Zaragoza, Spain |