English

Determinacy and reflection principles in second-order arithmetic

Logic 2023-05-22 v2

Abstract

It is known that several variations of the axiom of determinacy play important roles in the study of reverse mathematics, and the relation between the hierarchy of determinacy and comprehension are revealed by Tanaka, Nemoto, Montalb\'an, Shore, and others. We prove variations of a result by Ko{\l}odziejczyk and Michalewski relating determinacy of arbitrary boolean combinations of Σ20\Sigma^0_2 sets and reflection in second-order arithmetic. Specifically, we prove that: over ACA0\mathsf{ACA}_0, Π21\Pi^1_2-Ref(ACA0)\mathsf{Ref}(\mathsf{ACA}_0) is equivalent to n.(Σ10)n\forall n.(\Sigma^0_1)_n-Det0\mathsf{Det}^*_0; Π31\Pi^1_3-Ref(Π11\mathsf{Ref}(\Pi^1_1-CA0)\mathsf{CA}_0) is equivalent to n.(Σ10)n\forall n.(\Sigma^0_1)_n-Det\mathsf{Det}; and Π31\Pi^1_3-Ref(Π21\mathsf{Ref}(\Pi^1_2-CA0)\mathsf{CA}_0) is equivalent to n.(Σ20)n\forall n.(\Sigma^0_2)_n-Det\mathsf{Det}. We also restate results by Montalb\'an and Shore to show that Π31\Pi^1_3-Ref(Z2)\mathsf{Ref}(\mathsf{Z}_2) is equivalent to n.(Σ30)n\forall n.(\Sigma^0_3)_n-Det\mathsf{Det} over ACA0\mathsf{ACA}_0.

Keywords

Cite

@article{arxiv.2209.04082,
  title  = {Determinacy and reflection principles in second-order arithmetic},
  author = {Leonardo Pacheco and Keita Yokoyama},
  journal= {arXiv preprint arXiv:2209.04082},
  year   = {2023}
}
R2 v1 2026-06-28T00:59:24.355Z