  We study auctions whose bidders are embedded in a social or economic network.
As a result, even bidders who do not win the auction themselves might derive
utility from the auction, namely, when a friend wins. On the other hand, when
an enemy or competitor wins, a bidder might derive negative utility. Such spite
and altruism will alter the bidding strategies. A simple and natural model for
bidders' utilities in these settings posits that the utility of a losing bidder
i as a result of bidder j winning is a constant (positive or negative) fraction
of bidder j's utility.
