1. Centro de Matemática e Aplicações Fundamentais, Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1649-003 Lisboa, Portugal
2. Faculty of Mathematics, University of Vienna, Nordbergstr. 15, 1090 Wien, Austria
3. Faculty of Mathematics, University of Vienna and Wolfgang Pauli Institute, Nordbergstr. 15, 1090 Wien, Austria
4. Johann Radon Institute for Computational and Applied Mathematics, Austrian Academy of Sciences, Altenbergerstr. 69, 4040 Linz, Austria