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Weak systems of determinacy and arithmetical quasi-inductive definitions

  • P. D. Welch (a1)


We locate winning strategies for various -games in the L-hierarchy in order to prove the following:

Theorem 1. KP + Σ2-Comprehension -Determinacy.”

Alternatively: “there is a β-model of -Determinacy.” The implication is not reversible. (The antecedent here may be replaced with instances of Comprehension with only -lightface definable parameters—or even weaker theories.)

Theorem 2. KP + Δ2-Comprehension + Σ2-Replacement + -Determinacy.

(Here AQI is the assertion that every arithmetical quasi-inductive definition converges.) Alternatively: -Determinacy.

Hence the theories: , and are in strictly descending order of strength.



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The Journal of Symbolic Logic
  • ISSN: 0022-4812
  • EISSN: 1943-5886
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