sig Key {} sig Special, Regular extends Key {} one sig Control, Shift, Option, Command extends Special {} sig KeyPress {keys: set Key, event: Event} {one keys & Regular} sig Event {} fact {setObject (KeyPress, keys)} Note the use of Singleton to model the special keys. A prison database system tracks pairs of inmates who must not be placed in the same cell (because they belong to opposing gangs...

This paper extends the theory of legal cartels to a¢ liated private value and common value environments, and applies the theory to explain joint bidding patterns in U.S. federal government o¤shore oil and gas lease auctions. We show that e¢ cient collusion is always possible in private value environments, but may not be in common value environments. In the latter case, fear of the winner’s curs...