Professor der Mathematik, Universität Bonn

Professor of Mathematics, University of Maryland

School of Mathematics, Cardiff University

Powell Chair and University Distinguished Professor, Texas A&M University

Professor of Mathematics, Universität Regensburg

State University of New York at Buffalo

Universität Göttingen

Department of Mathematics, Quaid-i-Azam University, Islamabad-Pakistan

Catedrático de Álgebra, Departamento de Matemáticas, Universidad de Cádiz (Spain)

University of Edinburgh