OIMU 2005 Problem 5
Arnaldo and Bernaldo play a game where they alternate saying natural numbers, and the winner is the one who says . In each turn except the first the possible moves are determined from the previous number in the following way: write the valid numbers are the elements of . That way, for example, after Arnaldo says , Bernaldo must respond with , or .
We define the sets in the following way. We have iff Arnaldo, saying in his first turn, has a winning strategy; analogously, we have iff Bernaldo has a winning strategy if Arnaldo says during his first turn. This way, Define by . For example, and . Find
Dataset text AI-MO AoPS. Quoted with source.
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