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We unveil new patterns of Structural Reflection in the large-cardinal hierarchy below the first measurable cardinal. Namely, we give two different characterizations of strongly unfoldable and subtle cardinals in terms of a weak form of the…

Logic · Mathematics 2023-11-07 Joan Bagaria , Philipp Lücke

We show that the consistency strength of $\kappa$ being $2^\kappa$-square compact is at least weak compact and strictly less than indescribable. This is the first known improvement to the upper bound of strong compactness obtained in 1973…

Logic · Mathematics 2020-04-09 David Buhagiar , Mirna Džamonja

A cardinal is weakly Reinhardt if it is the critical point of an elementary embedding from the universe of sets into a model that contains the double powerset of every ordinal. This note establishes the equiconsistency of a proper class of…

Logic · Mathematics 2021-07-29 Gabriel Goldberg

Many set theorists point to the linearity phenomenon in the hierarchy of consistency strength, by which natural theories tend to be linearly ordered and indeed well ordered by consistency strength. Why should it be linear? In this paper I…

Logic · Mathematics 2022-08-29 Joel David Hamkins

We discuss the existence of complete accumulation points of sequences in products of topological spaces. Then we collect and generalize many of the results proved in Parts I, II and IV. The present Part VI is complementary to Part V to the…

Logic · Mathematics 2009-04-22 Paolo Lipparini

We share both recent and older, well-known results regarding the notions of stable ordinals and shrewd cardinals. We then argue that $\Sigma_2$-nonprojectible ordinals may be considered as recursive analogues to subtle cardinals, a highly…

Logic · Mathematics 2024-07-09 Jayde Sylvie Massmann

Starting with two supercompact cardinals we produce a generic extension of the universe in which a principle that we call ${\rm GM}^+(\omega_3,\omega_1)$ holds. This principle implies ${\rm ISP}(\omega_2)$ and ${\rm ISP}(\omega_3)$, and…

Logic · Mathematics 2019-05-21 Rahman Mohammadpour , Boban Velickovic

The motion of a composite system made of N particles is examined in a space with a canonical noncommutative algebra of coordinates. It is found that the coordinates of the center-of-mass position satisfy noncommutative algebra with…

General Relativity and Quantum Cosmology · Physics 2015-06-19 Kh. P. Gnatenko

We show that Vopenka's Principle and Vopenka cardinals are indestructible under reverse Easton forcing iterations of increasingly directed-closed partial orders, without the need for any preparatory forcing. As a consequence, we are able to…

Logic · Mathematics 2012-02-28 Andrew D. Brooke-Taylor

We characterize exactly the compactness properties of the product of \kappa\ copies of the space \omega\ with the discrete topology. The characterization involves uniform ultrafilters, infinitary languages, and the existence of nonstandard…

General Topology · Mathematics 2016-08-30 Paolo Lipparini

We introduce a new compactness principle which we call the gluing property. For a measurable cardinal $\kappa$ and a cardinal $\lambda$, we say that $\kappa$ has the $\lambda$-gluing property if every sequence of $\lambda$-many…

Logic · Mathematics 2026-03-27 Yair Hayut , Alejandro Poveda

Menger conjectured that subsets of R with the Menger property must be ${\sigma}$-compact. While this is false when there is no restriction on the subsets of R, for projective subsets it is known to follow from the Axiom of Projective…

General Topology · Mathematics 2020-06-30 Franklin D. Tall , Stevo Todorcevic , Seçil Tokgöz

We succeed to say something on the identities of (mu^+, mu) when mu>theta>cf(mu), mu strong limit theta--compact. This hopefully will help to prove the consistency of ``some pair (mu^+,mu) is not compact'', however, this has not been…

Logic · Mathematics 2007-05-23 Saharon Shelah

The concept of convex compactness, weaker than the classical notion of compactness, is introduced and discussed. It is shown that a large class of convex subsets of topological vector spaces shares this property and that is can be used in…

Functional Analysis · Mathematics 2010-06-02 Gordan Zitkovic

We show the existence of rigid combinatorial objects which previously were not known to exist. Specifically, for a wide range of the underlying parameters, we show the existence of non-trivial orthogonal arrays, $t$-designs, and $t$-wise…

Combinatorics · Mathematics 2017-03-14 Greg Kuperberg , Shachar Lovett , Ron Peled

We prove the consistency of: for suitable strongly inaccessible cardinal lambda the dominating number, i.e. the cofinality of lambda^lambda is strictly bigger than cov(meagre_lambda), i.e. the minimal number of nowhere dense subsets of…

Logic · Mathematics 2022-09-07 Saharon Shelah

We introduce the class of unshreddable theories, which contains the simple and NIP theories, and prove that such theories have exactly saturated models in singular cardinals, satisfying certain set-theoretic hypotheses. We also give…

Logic · Mathematics 2021-04-19 Itay Kaplan , Nicholas Ramsey , Saharon Shelah

A compactness theorem is proved for a family of K\"{a}hler surfaces with constant scalar curvature and volume bounded from below, diameter bounded from above, Ricci curvature bounded and the signature bounded from below. Furthermore, a…

Differential Geometry · Mathematics 2013-04-04 Hongliang Shao

Exacting and ultraexacting cardinals are large cardinal numbers compatible with the Zermelo-Fraenkel axioms of set theory, including the Axiom of Choice. In contrast with standard large cardinal notions, their existence implies that the…

Logic · Mathematics 2025-09-15 Juan Pablo Aguilera , Joan Bagaria , Gabriel Goldberg , Philipp Lücke

The paper settles the problem of the consistency of the existence of a single universal graph between a strong limit singular and its power. Assuming that in a model of $\mathbf{GCH}$ $\kappa$ is supercompact and the cardinals $\theta <…

Logic · Mathematics 2022-01-04 Márk Poór , Saharon Shelah