English

Strong Projective Witnesses

Logic 2026-01-14 v1

Abstract

We show Shelah's original creature forcing from 1984 strongly preserves tight mad families. In particular, answering questions of Fischer and Friedman and Friedman and Zdomskyy, we show the constellation 1=a<s=2\aleph_1 = \mathfrak{a} < \mathfrak{s} = \aleph_2 is consistent with the existence of a Δ31\Delta_3^1 wellorder of the reals and tight mad families of sizes 1,2\aleph_1, \aleph_2 which are Π11,Π21\Pi_1^1, \Pi_2^1-definable, respectively. Each of these projective definitions is of minimal possible complexity.

Cite

@article{arxiv.2601.08718,
  title  = {Strong Projective Witnesses},
  author = {Vera Fischer and Julia Millhouse},
  journal= {arXiv preprint arXiv:2601.08718},
  year   = {2026}
}

Comments

40 pages, submitted

R2 v1 2026-07-01T09:03:03.597Z