Virtual Nash Implementation with Admissible Supports

A social choice correspondence (SCC) is virtually implementable if it is epsilon-close (in the probability simplex) to some (exactly) implementable correspondence [Abreu, D., Sen, A., 1991, Virtual Implementation in Nash Equilibrium. Econometrica 59, 997-1021] proved that, without restriction on the set of alternatives receiving strictly positive probability at equilibrium, every SCC is virtually implementable in Nash Equilibrium. We study virtual implementation when the supports of equilibrium lotteries are restricted. We provide a necessary and sufficient condition, imposing joint restrictions on SCCs and admissible supports. Next, we discuss how to construct supports, and we underline an important difficulty. Finally, we study virtual implementation when the support is restricted to the efficient or individually rational alternatives.