Clément Carbonnier University of Cergy-Pontoise, THEMA and Sciences Po, LIEPP   Université de Cergy-Pontoise - THEMA 33 bd du Port Cergy-Pontoise, 95000 France   clement.carbonnier@u-cergy.fr   http://carbonnier-eco.w.pw/index-en.htm           JEL Areas: H2 : Taxation, Subsidies, and Revenue: General D4 : Market Structure and Pricing: General