{. Baumgärtner, and {. Winkler. Discussion paper series / Universität Heidelberg, Department of Economics Univ., Wirtschaftswiss. Fak., Heidelberg, (2000)
{. Reati. Economic papers / European Commission, Directorate-General for Economic and Financial Affairs Europ. Commission, Directorate-General for Economic and Financial Affairs, Brussels, (1995)