Maria gabriella Graziano Dept Mathematics and Statistics and CSEF - Centre for Studies in Economics and Finance   via Cinthia, Complesso Monte S.Angelo Naples, 80126   mgrazian@unina.it   http://www.csef.it/people/graziano.htm           JEL Areas: D5 : General Equilibrium and Disequilibrium: General H4 : Publicly Provided Goods: General