Models of interaction

The present Technical Report contains two papers that have been accepted at the S.I.N.G. 4 Conference, Wroklav, Poland, 26-28 June 2008.
Both papers have been also presented in seminars at the Computer Science Department, the former on June 3 2008 and the latter on January 23 2008.
The first paper presents the use of auction mechanisms for the allocation of chores instead of goods.
The latter paper presents and analyzes a small set of models that can be used by two players for the barter of goods without the intervention of any numerary good.