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An alternative mathematics based on qualitative plurality of finiteness is developed to make non-standard mathematics independent of infinite set theory. The vague concept "accessibility" is used coherently within finite set theory whose…

General Mathematics · Mathematics 2012-06-14 Toru Tsujishita

Let T be the family of open subsets of a topological space (not necessarily Hausdorff or even T_0). We prove that if T has a countable base and is not countable, then T has cardinality at least continuum.

Logic · Mathematics 2008-02-03 Saharon Shelah

Our theme is that not every interesting question in set theory is independent of $ZFC$. We give an example of a first order theory $T$ with countable $D(T)$ which cannot have a universal model at $\aleph_1$ without CH; we prove in $ZFC$ a…

Logic · Mathematics 2009-09-25 Menachem Kojman , Saharon Shelah

In this paper, methods of second order and higher order reverse mathematics are applied to versions of a theorem of Banach that extends the Schroeder-Bernstein theorem. Some additional results address statements in higher order arithmetic…

Logic · Mathematics 2023-11-15 Jeffry L. Hirst , Carl Mummert

Continuity of measure asserts that the measure of the union of an increasing sequence of sets is equal to the supremum of the measures of those sets. We provide counter examples in the case of uncountable unions. We construct the first…

Probability · Mathematics 2025-09-10 Simranjeet Bilkhu , Noah Mills Forman

We provide a formal introduction into the classic theorems of general topology and its axiomatic foundations in set theory. Starting from ZFC, the exposition in this first part includes relation and order theory as well as a construction of…

History and Overview · Mathematics 2013-06-26 Felix Nagel

This work is motivated by the problem of finding the limit of the applicability of the first incompleteness theorem ($\sf G1$). A natural question is: can we find a minimal theory for which $\sf G1$ holds? We examine the Turing degree…

Logic · Mathematics 2025-10-07 Yong Cheng

It is well known that in Zermelo-Fraenkel (ZF) set theory any finite set is decidable. In this paper we discuss an extension of ZF where this result is no longer valid. Such an extension is quasi-set theory and it has its origin on problems…

Quantum Physics · Physics 2007-05-23 Adonai S. Sant'Anna

The concept of measurement is discussed. It is argued that counting process in mathematics is also measurement which requires a basic unit. The idea of scale is put forward. The basic unit itself, which are composed of the infinitesimal of…

Quantum Physics · Physics 2007-05-23 Zhen Wang

In the absence of the axiom of choice, the set-theoretic status of many natural statements about metrizable compact spaces is investigated. Some of the statements are provable in $\mathbf{ZF}$, some are shown to be independent of…

General Topology · Mathematics 2020-08-05 Kyriakos Keremedis , Eleftherios Tachtsis , Eliza Wajch

We formalize an existing computability-theoretic method of presenting first-order structures whose domains have the cardinality of the continuum. Work using these methods until now has emphasized their topological properties. We shift the…

Logic · Mathematics 2025-11-07 Jason Block , Russell Miller

Goodstein sequences are numerical sequences in which a natural number m, expressed as the complete normal form to a given base a, is modified by increasing the value of the base a by one unit and subtracting one unit from the resulting…

General Mathematics · Mathematics 2009-07-28 Juan A. Perez

Usual math sets have special types: countable, compact, open, occasionally Borel, rarely projective, etc. Each such set is described by a single Set Theory formula with parameters unrelated to other formulas. Exotic expressions involving…

Logic in Computer Science · Computer Science 2026-04-01 Leonid A. Levin

We show that Morley's theorem on the number of countable models of a countable first-order theory becomes an undecidable statement when extended to second-order logic. More generally, we calculate the number of equivalence classes of…

Logic · Mathematics 2023-07-06 Christopher J. Eagle , Clovis Hamel , Sandra Müller , Franklin D. Tall

Within the framework of Zermelo-Fraenkel set theory without the Axiom of Choice, we establish equivalents to the assertion "the union of a countable collection of finite sets is countable" in the context of metric spaces, probability…

Logic · Mathematics 2023-08-24 Ilijas Farah , Jeffrey Marshall-Milne

We show that the theory ZFC-, consisting of the usual axioms of ZFC but with the power set axiom removed-specifically axiomatized by extensionality, foundation, pairing, union, infinity, separation, replacement and the assertion that every…

Logic · Mathematics 2015-08-05 Victoria Gitman , Joel David Hamkins , Thomas A. Johnstone

We study first-order expansions of the reals which do not define the set of natural numbers. We also show that several stronger notions of tameness are equivalent to each others.

Logic · Mathematics 2011-04-12 Antongiulio Fornasiero

This article explores the model-dependent nature of set cardinality, emphasizing that cardinality is not absolute but varies across different axiomatic frameworks. Although Cantor's diagonal argument shows the real numbers are…

Logic · Mathematics 2025-06-10 Slavica Mihaljevic Vlahovic , Branislav Dobrasin Vlahovic

Assuming the Continuum Hypothesis, there is a compact first countable connected space of weight aleph_1 with no totally disconnected perfect subsets. Each such space, however, may be destroyed by some proper forcing order which does not add…

General Topology · Mathematics 2007-05-23 Joan E. Hart , Kenneth Kunen

All constructive methods employed in modern mathematics produce only countable sets, even when designed to transcend countability. We show that any constructive argument for uncountability -- excluding diagonalization techniques --…

General Mathematics · Mathematics 2025-05-28 Stanislav Semenov