English

Bounding 2D Functions by Products of 1D Functions

Logic 2026-04-24 v7

Abstract

Given sets X,YX,Y and a regular cardinal μ\mu, let Φ(X,Y,μ)\Phi(X,Y,\mu) be the statement that for any function f:X×Yμf : X \times Y \to \mu, there are functions g1:Xμg_1 : X \to \mu and g2:Yμg_2 : Y \to \mu such that or all (x,y)X×Y(x,y) \in X \times Y, f(x,y)max{g1(x),g2(y)}.f(x,y) \le \max \{ g_1(x), g_2(y) \}. In ZFC, the statement Φ(ω1,ω1,ω)\Phi(\omega_1, \omega_1, \omega) is false. However, we show the theory ZF + ``the club filter on ω1\omega_1 is normal'' + Φ(ω1,ω1,ω)\Phi(\omega_1, \omega_1, \omega) (which is implied by ZF + AD) implies that for every α<ω1\alpha < \omega_1 there is a κ(α,ω1)\kappa \in (\alpha,\omega_1) such that in some inner model, κ\kappa is measurable with Mitchell order α\ge \alpha. There was an error in Welch's paper ``Characterizing Subsets of ω1\omega_1 Constructible From a Real'', which he has retracted in a personal communication. Our paper originally referenced that paper. In this version of our paper, we are not using that result. Our consistency strength upper bound has changed accordingly.

Keywords

Cite

@article{arxiv.1601.05454,
  title  = {Bounding 2D Functions by Products of 1D Functions},
  author = {François Dorais and Dan Hathaway},
  journal= {arXiv preprint arXiv:1601.05454},
  year   = {2026}
}

Comments

17 pages

R2 v1 2026-06-22T12:33:46.426Z