Let M(X) be a family of all equivalent local martingale measures for some locally bounded d-dimensional process X, and V be a positive process. Main result of the paper (Theorem 2.1) states that the process V is a supermartingale whatever Q in M(X), if and only if this process admits the...

We propose a simple mechanism that might improve voluntary contributions to public goods. Using a laboratory experiment we analyze how bundling public with private goods affects individuals' valuations for both goods. In the experiment, subjects may purchase a private and a public good either...