Aysegul YILDIZ CERMSEM-Universite de Paris 1-Galatasaray Universitesi   106-112, bd de l'Hopital Paris, 75013 France   ayildiz@univ-paris1.fr   http://cermsem.univ-paris1.fr/yildiz/yildiz-english.htm           JEL Areas: D5 : General Equilibrium and Disequilibrium: General C0 : Mathematical and Quantitative Methods: General