Cuong Le van CES, CNRS, University Paris 1   CES 106 boulevard de l'Hopital Paris, 75013 France   levan@univ-paris1.fr     Biographical Sketch: Director of Research, French National Center of Research Doctor in Mathematics       JEL Areas: O4 : Economic Growth and Aggregate Productivity: General D5 : General Equilibrium and Disequilibrium: General