Auctioning or assigning an object: some remarkable VCG mechanisms ´ HERVE MOULIN Rice University 1. AUCTIONING A GOOD A second price Vickrey auction is a simple mechanism to transfer a valuable object (a good) between a seller and n potential buyers. It treats buyers fairly, elicits their truthful valuations for the good, and allocates the good e ciently. But the division of the surplus between the seller and the buyers is hardly compelling. Writing a k for the k-th highest valuation among buyers, and setting without loss of generality the seller s valuation at zero, of the total surplus a 1 the seller gets a 2 and the buyers a 1 a 2 , thus either share can be arbitrarily large or small, depending on the distribution of valuations. Moreover at most one buyer gets any surplus at all. The familiar Vickrey-Clarke-Groves (thereafter VCG, see [Green and La ont 1979]) mechanisms preserve the incentives and e ciency properties of the Vickrey auction, but allow more exibility in the division of the surplus. Suppose that explicit guidelines regulate the division of surplus: the seller should get a 1 , the buyers (1 )a 1 . We construct
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