Monday, November 19, 2007
4:00 PM
5130 Upson Hall
  Theory Seminar
Fall 2007
CS 789

Itai Ashlagi


Position Auctions and Mediators


This talk consists of two parts:

1.  We show that weighted VCG are the only truthful-revealing symmetric position auctions.

2. A mediator is a reliable entity, which plays on behalf of the players who give her the right of play. The mediator is guaranteed to behave in a pre-specified way based on messages received from the agents.

However, a mediator can not enforce behavior; that is, agents can play in the game directly without the mediator's help.  A mediator generates a new game for the players, the mediated game. The outcome in the original game of an equilibrium in the mediated game is called a mediated equilibrium. Monderer and Tennenholtz defined a mediator for games with complete information. We extend the theory of mediators to games with incomplete information, and use the new theory to study position auctions, a central topic in practical and theoretical electronic commerce. We provide minimal sets of conditions on position auctions, which are sufficient to guarantee that the VCG outcome function is a mediated equilibrium in these position auctions.