  Consider an abstract social choice setting with incomplete information, where
the number of alternatives is large. Albeit natural, implementing VCG
mechanisms may not be feasible due to the prohibitive communication
constraints. However, if players restrict attention to a subset of the
alternatives, feasibility may be recovered.
  This paper characterizes the class of subsets which induce an ex-post
equilibrium in the original game. It turns out that a crucial condition for
such subsets to exist is the existence of a type-independent optimal social
alternative, for each player. We further analyze the welfare implications of
these restrictions.
  This work follows work by Holzman, Kfir-Dahav, Monderer and Tennenholtz
(2004) and Holzman and Monderer (2004) where similar analysis is done for
combinatorial auctions.
