Approximate robustness of equilibrium to incomplete information

摘要

We relax the Kajii and Morris (Econometrica 65:1283-1309, 1997a) notion of equilibrium robustness by allowing approximate equilibria in close incomplete information games. The new notion is termed "approximate robustness". The approximately robust equilibrium correspondence turns out to be upper hemicontinuous, unlike the (exactly) robust equilibrium correspondence. As a corollary of the upper hemicontinuity, it is shown that approximately robust equilibria exist in all two-player zero-sum games and all two-player two-strategy games, whereas (exactly) robust equilibria may fail to exist for some games in these categories.