LONG BOREL GAMES 3 Large Cardinal Axioms, Or Strengthenings of the Axiom of Infinity, and Use Them to Prove the Determinacy of Games on the Natural Numbers
LONG BOREL GAMES J. P. AGUILERA Abstract. We study games of length ω2 with moves in N and Borel payoff. These are, e.g., games in which two players alternate turns playing digits to produce a real number in [0, 1] infinitely many times, after which the winner is decided in terms of the sequence belonging to a Borel set in the product space [0, 1]N. The main theorem is that Borel games of length ω2 are determined if, and only if, for every countable ordinal α, there is a fine-structural, countably iterable model of Zermelo set theory with α-many iterated powersets above a limit of Woodin cardinals. Contents 1. Introduction 1 2. Preliminaries 5 3. Determinacy and L(R) 7 4. Proof of Lemma 3.1 18 5. Derived model theorems 25 References 28 1. Introduction Given a Borel subset A of the Hilbert space ℓ2, define a two-player perfect- information, zero-sum game in which Player I and Player II alternate turns playing 0 digits xi ∈{0, 1,..., 9} infinitely often, giving rise to a real number ∞ x0 x0 = i . X 10i+1 i=0 arXiv:1906.11757v1 [math.LO] 27 Jun 2019 Afterwards, they continue alternating turns to produce real numbers x1, x2, and so on. To ensure that the sequence belongs to ℓ2, we normalize, e.g., by setting xi yi = . i +1 Player I wins the game if, and only if, ~y ∈ A; otherwise Player II wins. These are games of transfinite length ω2. (Recall that ω denotes the order-type of the natural numbers.) It is a natural question whether these games are determined, i.e., whether one of the players has a winning strategy.
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