Announcement-and-challenge covering of a closed payoff
ID: announcement-and-challenge-covering-of-a-closed-payoff
After a fixed even-depth prefix, Player I announces a move and a set of first exit positions from a closed set of infinite plays. Player II accepts, or challenges an exit . Acceptance follows the old game until the first exit, where I wins exactly when that exit belongs to . A challenge forces play through and then resumes the old game. Infinite accepted plays remain in the closed payoff; infinite challenged plays are outside it. Thus the pulled-back payoff is clopen. For an I-strategy, transfer by initially accepting and switching to the challenged simulation at an exit in . For an II-strategy, announce the set of exits that this strategy never challenges under any announcement; it must accept this set. An exit outside it permits a challenged simulation, while an exit inside it is a premature loss for II. These maps prove the game covering lifting condition, rather than merely continuity of the projection.
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