1. a Institute of Applied Mathematics , University of Bonn , Bonn, Germany, BiBoS, University of Bonn, Bonn, Germany, SF B611, University of Bielefeld and University of Bonn, Bielefeld, Bonn, Germany, Acc. Architettura (USI), Mendrisio, Switzerland, and Department of Mathematics, University of Trento, Trento , Italy
2. b Departments of Mathematics and Computer Science , University of Camerino, Camerino (MC), Italy and Institute of Applied Mathematics, University of Bonn , Bonn , Germany