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arXiv · 2505.00414

Ladders and Squares

Lorenzo Notaro
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Abstract

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

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BibTeXRIS

Lorenzo Notaro. 2025-11-20. Ladders and Squares. https://doi.org/10.1016/j.aim.2025.110714

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