An auction is externality-robust if unilateral deviations from equilibrium leave the other bidders’ payoffs unaffected. The equilibrium and its outcome will then persist if certain types of externalities arise between bidders. One example are externalities due to spiteful preferences, which...

A nudge is a non-coercive paternalistic intervention that attempts to improve choices by manipulating the framing of a decision problem. As any paternalism, it faces the difficulty of determining the appropriate welfare criterion. We propose a welfare-theoretic foundation for nudging similar in...