1. Assistant Professor, Dept. of Logistics, Institute of Applied Mathematics, Wroclaw Univ. of Economics, ul. Komandorska 118/120, 53-345 Wroclaw, Poland (corresponding author).
2. Associate Professor, Faculty of Business and Law, Dept. of Accounting, Economics and Finance, Swinburne Univ. of Technology, BA Bldg., John St., Hawthorn, VIC 3122, Australia.