English

Tukey-order with models on Pawlikowski's theorems

Logic 2021-09-03 v1

Abstract

In J. Symbolic Logic,51(4): 957-968, 1986, Pawlikowski proved that, if rr is a random real over N\mathbf{N}, and cc is Cohen real over N[r]\mathbf{N}[r], then (a) in N[r][c]\mathbf{N}[r][c] there is a Cohen real over N[c]\mathbf{N}[c], and (b) 2ωN[c]NN[r][c]2^\omega\cap\mathbf{N}[c]\notin\mathcal{N}\cap\mathbf{N}[r][c], so in N[r][c]\mathbf{N}[r][c] there is no random real over N[c]\mathbf{N}[c]. To prove this, Pawlikowski proposes the following notion: Given two models NM\mathbf{N}\subseteq \mathbf{M} of ZFC, we associate with a cardinal characteristic x\mathfrak{x} of the continuum, a sentence xNM\mathfrak{x}_\mathbf{N}^\mathbf{M} saying that in M\mathbf{M}, the reals in N\mathbf{N} give an example of a family fulfilling the requirements of the cardinal. So to prove (a) and (b), it suffices to prove that (a') cov(M)N[c]M[c]cof(M)NMcov(N)NM\mathrm{cov}(\mathcal{M})_{\mathbf{N}[c]}^{\mathbf{M}[c]}\Rightarrow\mathrm{cof}(\mathcal{M})_{\mathbf{N}}^{\mathbf{M}}\Rightarrow\mathrm{cov}(\mathcal{N})_{\mathbf{N}}^{\mathbf{M}}, and (b') cov(M)NMadd(M)NMnon(M)N[c]M[c]cov(N)N[c]M[c]\mathrm{cov}(\mathcal{M})_\mathbf{N}^\mathbf{M}\Rightarrow\mathrm{add}(\mathcal{M})_{\mathbf{N}}^{\mathbf{M}}\Rightarrow\mathrm{non}(\mathcal{M})_{\mathbf{N}[c]}^{\mathbf{M}[c]}\Rightarrow\mathrm{cov}(\mathcal{N})_{\mathbf{N}[c]}^{\mathbf{M}[c]}. In this paper, we introduce the notion of Tukey-order with models, which expands the concept of Tukey-order introduced by Vojt\'{a}\v{s} (Israel Math. Conf. Proc. 6: 619-643, 1991) to prove expressions of the form xNMyNM\mathfrak{x}_\mathbf{N}^\mathbf{M}\Rightarrow\mathfrak{y}_\mathbf{N}^\mathbf{M}. In particular, we show (a') and (b') using Tukey-order with models.

Cite

@article{arxiv.2109.00736,
  title  = {Tukey-order with models on Pawlikowski's theorems},
  author = {Miguel A. Cardona},
  journal= {arXiv preprint arXiv:2109.00736},
  year   = {2021}
}

Comments

17 pages, 4 figures. RIMS Set Theory Workshop: Reals and Topology. November 16 - 20, 2020

R2 v1 2026-06-24T05:37:03.257Z