In many online systems, individuals provide services for each other; the recipient of the service obtains a benefit but the provider of the service incurs a cost. If benefit exceeds cost, provision of the service increases social welfare and should therefore be encouraged—but the individuals...

Much of the lending in modern economies is secured by some form of collateral: residential and commercial mortgages and corporate bonds are familiar examples. This paper builds an extension of general equilibrium theory that incorporates durable goods, collateralized securities, and the...

Most of the literature argues that competitive analysis has nothing interesting to say about location. This paper argues, to the contrary, that a competitive model can have something interesting to say about location, provided that locations are not identical and transportation costs are not...