1. De la Mesure de l'Utilité des Travaux Publics;Dupuit;Annales des ponts et Chaussées,1844
2. External Economics and Diseconomies,;Ellis;American Economic Review,1943
3. The Marshallian Demand Curve,;Friedman;Journal of Political Economy,1949
4. Milton Friedman , Price Theory, Chicago, 1976.