1. Department of Mathematics; INESC Coimbra and Viseu Polytechnic Institute; Campus Politécnico de Viseu 3504-510 Viseu Portugal
2. INESC Coimbra; Faculty of Economics; University of Coimbra; Av Dias da Silva 165 3004-512 Coimbra Portugal
3. Department of Business Administration; University of Vienna; Oskar Morgenstern Platz 1 A-1090 Vienna Austria