Affiliation: | 1.Fakult?t für Mathematik, Ruhr-Universit?t Bochum, 44780, Bochum, Germany ;2.Lehrstuhl für Algebra und Zahlentheorie, RWTH Aachen University, 52062, Aachen, Germany ;3.School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne, UK ; |