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##### An unpublished theorem of Solovay on OD partitions of reals into two non-OD parts, revisited with Ali Enayat Journal of Mathematical Logic 2150014. forthcoming.
A definable pair of disjoint non-OD sets of reals exists in the Sacks and [Formula: see text]o-large generic extensions of the constructible universe L. More specifically, if [Formula: see text] is either Sacks generic or [Formula: see text]o generic real over L, then it is true in L[Formula: see text] that there is a lightface [Formula: see text] equivalence relation Q on the [Formula: see text] set [Formula: see text] with exactly two equivalence classes, and both those classes are non-OD sets…Read more
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##### Canonization of Smooth Equivalence Relations on Infinite-Dimensional $mathsf{E}_{0}$-Large Products with Vassily Lyubetsky Notre Dame Journal of Formal Logic 61 (1): 117-128. 2020.
We propose a canonization scheme for smooth equivalence relations on Rω modulo restriction to E0-large infinite products. It shows that, given a pair of Borel smooth equivalence relations E, F on Rω, there is an infinite E0-large perfect product P⊆Rω such that either F⊆E on P, or, for some ℓ
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##### Countable OD sets of reals belong to the ground model with Vassily Lyubetsky Archive for Mathematical Logic 57 (3-4): 285-298. 2018.
It is true in the Cohen, Solovay-random, dominaning, and Sacks generic extension, that every countable ordinal-definable set of reals belongs to the ground universe. It is true in the Solovay collapse model that every non-empty OD countable set of sets of reals consists of \ elements.
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##### Cauchy’s Infinitesimals, His Sum Theorem, and Foundational Paradigms with Tiziana Bascelli, Piotr Błaszczyk, Alexandre Borovik, Karin U. Katz, Mikhail G. Katz, Semen S. Kutateladze, Thomas McGaffey, David M. Schaps, and David Sherry Foundations of Science 23 (2): 267-296. 2018.
Cauchy's sum theorem is a prototype of what is today a basic result on the convergence of a series of functions in undergraduate analysis. We seek to interpret Cauchy’s proof, and discuss the related epistemological questions involved in comparing distinct interpretive paradigms. Cauchy’s proof is often interpreted in the modern framework of a Weierstrassian paradigm. We analyze Cauchy’s proof closely and show that it finds closer proxies in a different modern framework.
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##### Gregory’s Sixth Operation with Tiziana Bascelli, Piotr Błaszczyk, Karin U. Katz, Mikhail G. Katz, Semen S. Kutateladze, Tahl Nowik, David M. Schaps, and David Sherry Foundations of Science 23 (1): 133-144. 2018.
In relation to a thesis put forward by Marx Wartofsky, we seek to show that a historiography of mathematics requires an analysis of the ontology of the part of mathematics under scrutiny. Following Ian Hacking, we point out that in the history of mathematics the amount of contingency is larger than is usually thought. As a case study, we analyze the historians’ approach to interpreting James Gregory’s expression ultimate terms in his paper attempting to prove the irrationality of \. Here Gregory…Read more
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##### What Makes a Theory of Infinitesimals Useful? A View by Klein and Fraenkel with K. Katz, M. Katz, and Thomas Mormann Journal of Humanistic Mathematics 8 (1). 2018.
Felix Klein and Abraham Fraenkel each formulated a criterion for a theory of infinitesimals to be successful, in terms of the feasibility of implementation of the Mean Value Theorem. We explore the evolution of the idea over the past century, and the role of Abraham Robinson's framework therein.
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##### Controversies in the Foundations of Analysis: Comments on Schubring’s Conflicts with Piotr Błaszczyk, Mikhail G. Katz, and David Sherry Foundations of Science 22 (1): 125-140. 2017.
Foundations of Science recently published a rebuttal to a portion of our essay it published 2 years ago. The author, G. Schubring, argues that our 2013 text treated unfairly his 2005 book, Conflicts between generalization, rigor, and intuition. He further argues that our attempt to show that Cauchy is part of a long infinitesimalist tradition confuses text with context and thereby misunderstands the significance of Cauchy’s use of infinitesimals. Here we defend our original analysis of various m…Read more
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##### On external Scott algebras in nonstandard models of peano arithmetic Journal of Symbolic Logic 61 (2): 586-607. 1996.
We prove that a necessary and sufficient condition for a countable set L of sets of integers to be equal to the algebra of all sets of integers definable in a nonstandard elementary extension of ω by a formula of the PA language which may include the standardness predicate but does not contain nonstandard parameters, is as follows: L is closed under arithmetical definability and contains 0 (ω) , the set of all (Gödel numbers of) true arithmetical sentences. Some results related to definability o…Read more
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##### Internal Approach to External Sets and Universes: Part 3: Partially Saturated Universes with Michael Reeken Studia Logica 56 (3): 293-322. 1996.
In this article ‡ we show how the universe of HST, Hrbaček set theory admits a system of subuniverses which keep the Replacement, model Power set and Choice, and also keep as much of Saturation as it is necessary. This gives sufficient tools to develop the most complicated topics in nonstandard analysis, such as Loeb measures.
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##### An Ulm-Type Classification Theorem for Equivalence Relations in Solovay Model Journal of Symbolic Logic 62 (4): 1333-1351. 1997.
We prove that in the Solovay model, every OD equivalence relation, E, over the reals, either admits an OD reduction to the equality relation on the set of all countable binary sequences, or continuously embeds $\mathrm{E}_0$, the Vitali equivalence. If E is a $\Sigma^1_1$ relation then the reduction above can be chosen in the class of all $\triangle_1$ functions. The proofs are based on a topology generated by OD sets.
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##### A definable E 0 class containing no definable elements with Vassily Lyubetsky Archive for Mathematical Logic 54 (5-6): 711-723. 2015.
A generic extension L[x]\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathbf{L}[x]}$$\end{document} by a real x is defined, in which the E0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgree…Read more
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##### Special Model Axiom in Nonstandard Set Theory with Michael Reeken Mathematical Logic Quarterly 45 (3): 371-384. 1999.
We demonstrate that the special model axiom SMA of Ross admits a natural formalization in Kawai's nonstandard set theory KST but is independent of KST. As an application of our methods to classical model theory, we present a short proof of the consistency of the existence of a k+ like k-saturated model of PA for a given cardinal k
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##### Linearization of definable order relations Annals of Pure and Applied Logic 102 (1-2): 69-100. 2000.
We prove that if ≼ is an analytic partial order then either ≼ can be extended to a Δ 2 1 linear order similar to an antichain in 2 ω 1 , ordered lexicographically, or a certain Borel partial order ⩽ 0 embeds in ≼. Similar linearization results are presented, for κ -bi-Souslin partial orders and real-ordinal definable orders in the Solovay model. A corollary for analytic equivalence relations says that any Σ 1 1 equivalence relation E , such that E 0 does not embed in E , is fully determined by i…Read more
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##### Extending standard models of ZFC to models of nonstandard set theories with Michael Reeken Studia Logica 64 (1): 37-59. 2000.
We study those models of ZFCwhich are embeddable, as the class of all standard sets, in a model of internal set theory &gt;ISTor models of some other nonstandard set theories.
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##### Leibniz versus Ishiguro: Closing a Quarter Century of Syncategoremania with Tiziana Bascelli, Piotr Błaszczyk, Karin U. Katz, Mikhail G. Katz, David M. Schaps, and David Sherry Hopos: The Journal of the International Society for the History of Philosophy of Science 6 (1): 117-147. 2016.
Did Leibniz exploit infinitesimals and infinities à la rigueur or only as shorthand for quantified propositions that refer to ordinary Archimedean magnitudes? Hidé Ishiguro defends the latter position, which she reformulates in terms of Russellian logical fictions. Ishiguro does not explain how to reconcile this interpretation with Leibniz’s repeated assertions that infinitesimals violate the Archimedean property (i.e., Euclid’s Elements, V.4). We present textual evidence from Leibniz, as well a…Read more
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##### On non-wellfounded iterations of the perfect set forcing Journal of Symbolic Logic 64 (2): 551-574. 1999.
We prove that if I is a partially ordered set in a countable transitive model M of ZFC then M can be extended by a generic sequence of reals a i , i ∈ I, such that ℵ M 1 is preserved and every a i is Sacks generic over \$\mathfrak{M}[\langle \mathbf{a}_j: j . The structure of the degrees of M-constructibility of reals in the extension is investigated. As applications of the methods involved, we define a cardinal invariant to distinguish product and iterated Sacks extensions, and give a short proo…Read more
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##### Internal Approach to External Sets and Universes: Part 2. External Universes over the Universe of Bounded Set Theory with Michael Reeken Studia Logica 55 (3): 347-376. 1995.
In this article we show how the universe of BST, bounded set theory can be enlarged by definable subclasses of sets so that Separation and Replacement are true in the enlargement for all formulas, including those in which the standardness predicate may occur. Thus BST is strong enough to incorporate external sets in the internal universe in a way sufficient to develop topics in nonstandard analysis inaccessible in the framework of a purely internal approach, such as Loeb measures.
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##### A version of the Jensen–Johnsbråten coding at arbitrary level n≥ 3 Archive for Mathematical Logic 40 (8): 615-628. 2001.
We generalize, on higher projective levels, a construction of “incompatible” generic Δ1 3 real singletons given by Jensen and Johnsbråten
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##### A definable nonstandard model of the reals with Saharon Shelah Journal of Symbolic Logic 69 (1): 159-164. 2004.
We prove, in ZFC,the existence of a definable, countably saturated elementary extension of the reals
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##### Tools, Objects, and Chimeras: Connes on the Role of Hyperreals in Mathematics with Mikhail G. Katz and Thomas Mormann Foundations of Science 18 (2): 259-296. 2013.
We examine some of Connes’ criticisms of Robinson’s infinitesimals starting in 1995. Connes sought to exploit the Solovay model S as ammunition against non-standard analysis, but the model tends to boomerang, undercutting Connes’ own earlier work in functional analysis. Connes described the hyperreals as both a “virtual theory” and a “chimera”, yet acknowledged that his argument relies on the transfer principle. We analyze Connes’ “dart-throwing” thought experiment, but reach an opposite conclus…Read more
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##### On Baire Measurable Homomorphisms of Quotients of the Additive Group of the Reals with Michael Reeken Mathematical Logic Quarterly 46 (3): 377-384. 2000.
The quotient ℝ/G of the additive group of the reals modulo a countable subgroup G does not admit nontrivial Baire measurable automorphisms