1. Department of Actuarial Mathematics and Statistics, Heriot Watt University, Edinburgh, EH14 4AS, UK.
2. School of Mathematical Sciences, University of Nottingham, Nottingham, NG72RD, UK.
3. School of Mathematical Sciences, SKLCAM and LMNS, Fudan University, 200433, Shanghai, China.
4. Institut für Mathematik, Julius-Maximilians-Universität Würzburg MU97074, Würzburg, Germany.