1. School of Mathematics, Maxwell Institute for Mathematical Sciences, The University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK
2. Centro de Matemática e Aplicações (CMA), FCT, UNL, Portugal
3. Department of Statistics and Econometrics, University of Erlangen-Nüremberg, Lange Gasse 20, 90403 Nuremberg, Germany
4. Moody's Analytics, 7 Exchange Crescent Conference Square, Edinburgh EH3 8RD, UK