English

Evitable iterates of the consistency operator

Logic 2022-09-21 v2

Abstract

Let's fix a reasonable subsystem TT of arithmetic; why are natural extensions of TT pre-well-ordered by consistency strength? In previous work, an approach to this question was proposed. The goal of this work was to classify the recursive functions that are monotone with respect to the Lindenabum algebra of TT. According to an optimistic conjecture, roughly, every such function must be equivalent to an iterate ConTα\mathsf{Con}_T^\alpha of the consistency operator in the limit. In previous work the author established the first case of this optimistic conjecture; roughly, every recursive monotone function is either as weak as the identity operator in the limit or as strong as ConT\mathsf{Con}_T in the limit. Yet in this note we prove that this optimistic conjecture fails already at the next step; there are recursive monotone functions that are neither as weak as ConT\mathsf{Con}_T in the limit nor as strong as ConT2\mathsf{Con}_T^2 in the limit. In fact, for every α\alpha, we produce a function that is cofinally as strong as ConTα\mathsf{Con}^\alpha_T yet cofinally as weak as ConT\mathsf{Con}_T.

Keywords

Cite

@article{arxiv.2202.01174,
  title  = {Evitable iterates of the consistency operator},
  author = {James Walsh},
  journal= {arXiv preprint arXiv:2202.01174},
  year   = {2022}
}
R2 v1 2026-06-24T09:16:16.962Z