APPROXIMATE ROBUSTNESS OF EQUILIBRIUM TO INCOMPLETE INFORMATION

We relax the Kajii and Morris (1997a) notion of equilibrium ro- bustness by allowing approximate equilibria in close incomplete infor- mation games. The new notion is termed "approximate robustness". The approximately robust equilibrium correspondence turns out to be upper hemicontinuous, unlike the (exactly) robust equilibrium corre- spondence. 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.