1. Department of Statistics; The University of Warwick; CV4 7AL Coventry UK
2. LAREMA UMR CNRS 6093; Université d'Angers; 2, Bd Lavoisier Angers Cedex 01 49045 France
3. Faculty of Pure and Applied Mathematics; Wrocław University of Science and Technology; Wybrzeże Wyspiańskiego 27 50-370 Wrocław Poland