Etienne Lehmann CRED - University Pantheon Assas (Paris 2) and CREST   15 boulevard Gabriel Péri 15 boulevard Gabriel Péri Malakoff Cedex, 92 245 France   etienne.lehmann@gmail.com   http://cred.u-paris2.fr/node/69           JEL Areas: H2 : Taxation, Subsidies, and Revenue: General J6 : Mobility, Unemployment, and Vacancies: General