English

Ladders and Squares

Logic 2025-12-01 v2 Combinatorics

Abstract

In 1984, Ditor asked two questions: (1) For each nωn\in\omega and infinite cardinal κ\kappa, is there a join-semilattice of breadth n+1n+1 and cardinality κ+n\kappa^{+n} whose principal ideals have cardinality <κ< \kappa? (2) For each nωn \in \omega, is there a lower-finite lattice of cardinality n\aleph_{n} whose elements have at most n+1n+1 lower covers? We show that both questions have positive answers under the axiom of constructibility, and hence consistently with ZFC\mathsf{ZFC}. More specifically, we derive the positive answers from assuming that κ\square_\kappa holds for enough κ\kappa's.

Keywords

Cite

@article{arxiv.2505.00414,
  title  = {Ladders and Squares},
  author = {Lorenzo Notaro},
  journal= {arXiv preprint arXiv:2505.00414},
  year   = {2025}
}

Comments

30 pages

R2 v1 2026-06-28T23:17:49.724Z