
827Tools, Objects, and Chimeras: Connes on the Role of Hyperreals in MathematicsFoundations of Science 18 (2): 259296. 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 nonstandard 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’ “dartthrowing” thought experiment, but reach an opposite conclus…Read more

310What Makes a Theory of Infinitesimals Useful? A View by Klein and FraenkelJournal 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.

281Is Leibnizian calculus embeddable in first order logic?Foundations of Science 22 (4). 2017.To explore the extent of embeddability of Leibnizian infinitesimal calculus in firstorder logic (FOL) and modern frameworks, we propose to set aside ontological issues and focus on pro cedural questions. This would enable an account of Leibnizian procedures in a framework limited to FOL with a small number of additional ingredients such as the relation of infinite proximity. If, as we argue here, first order logic is indeed suitable for developing modern proxies for the inferential moves found…Read more

140Internal approach to external sets and universesStudia Logica 55 (2). 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

91A nonstandard set theory in the $\displaystyle\in$ languageArchive for Mathematical Logic 39 (6): 403416. 2000.. We demonstrate that a comprehensive nonstandard set theory can be developed in the standard $\displaystyle{\in}$ language. As an illustration, a nonstandard ${\sf Law of Large Numbers}$ is obtained

81Internal Approach to External Sets and Universes: Part 3: Partially Saturated UniversesStudia Logica 56 (3): 293322. 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.

80A version of the Jensen–Johnsbråten coding at arbitrary level n≥ 3Archive for Mathematical Logic 40 (8): 615628. 2001.We generalize, on higher projective levels, a construction of “incompatible” generic Δ1 3 real singletons given by Jensen and Johnsbråten

48A definable nonstandard model of the realsJournal of Symbolic Logic 69 (1): 159164. 2004.We prove, in ZFC,the existence of a definable, countably saturated elementary extension of the reals

44Elementary extensions of external classes in a nonstandard universeStudia Logica 60 (2): 253273. 1998.In continuation of our study of HST, Hrbaek set theory (a nonstandard set theory which includes, in particular, the ZFC Replacement and Separation schemata in the stlanguage, and Saturation for wellorderable families of internal sets), we consider the problem of existence of elementary extensions of inner "external" subclasses of the HST universe.We show that, given a standard cardinal , any set R * generates an "internal" class S(R) of all sets standard relatively to elements of R, and an "e…Read more

44On nonwellfounded iterations of the perfect set forcingJournal of Symbolic Logic 64 (2): 551574. 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 Mconstructibility 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

40Uniqueness, collection, and external collapse of cardinals in ist and models of peano arithmeticJournal of Symbolic Logic 60 (1): 318324. 1995.We prove that in IST, Nelson's internal set theory, the Uniqueness and Collection principles, hold for all (including external) formulas. A corollary of the Collection theorem shows that in IST there are no definable mappings of a set X onto a set Y of greater (not equal) cardinality unless both sets are finite and #(Y) ≤ n #(X) for some standard n. Proofs are based on a rather general technique which may be applied to other nonstandard structures. In particular we prove that in a nonstandard mo…Read more

33An Ulmtype classification theorem for equivalence relations in Solovay modelJournal of Symbolic Logic 62 (4): 13331351. 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 (of length $ ) binary sequences, or continuously embeds E 0 , the Vitali equivalence. If E is a Σ 1 1 (resp. Σ 1 2 ) relation then the reduction above can be chosen in the class of all ▵ 1 (resp. ▵ 2 ) functions. The proofs are based on a topology generated by OD sets

30On external Scott algebras in nonstandard models of peano arithmeticJournal of Symbolic Logic 61 (2): 586607. 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

28Proofs and Retributions, Or: Why Sarah Can’t Take LimitsFoundations of Science 20 (1): 125. 2015.The small, the tiny, and the infinitesimal have been the object of both fascination and vilification for millenia. One of the most vitriolic reviews in mathematics was that written by Errett Bishop about Keisler’s book Elementary Calculus: an Infinitesimal Approach. In this skit we investigate both the argument itself, and some of its roots in Bishop George Berkeley’s criticism of Leibnizian and Newtonian Calculus. We also explore some of the consequences to students for whom the infinitesimal a…Read more

28Extending standard models of ZFC to models of nonstandard set theoriesStudia Logica 64 (1): 3759. 2000.We study those models of ZFCwhich are embeddable, as the class of all standard sets, in a model of internal set theory >ISTor models of some other nonstandard set theories.

26A NonStandard Analysis of a Cultural Icon: The Case of Paul HalmosLogica Universalis 10 (4): 393405. 2016.We examine Paul Halmos’ comments on category theory, Dedekind cuts, devil worship, logic, and Robinson’s infinitesimals. Halmos’ scepticism about category theory derives from his philosophical position of naive settheoretic realism. In the words of an MAA biography, Halmos thought that mathematics is “certainty” and “architecture” yet 20th century logic teaches us is that mathematics is full of uncertainty or more precisely incompleteness. If the term architecture meant to imply that mathematic…Read more

20Isomorphism property in nonstandard extensions of theZFC universeAnnals of Pure and Applied Logic 88 (1): 125. 1997.We study models of HST . This theory admits an adequate formulation of the isomorphism propertyIP, which postulates that any two elementarily equivalent internally presented structures of a wellorderable language are isomorphic. We prove that IP is independent of HST and consistent with HST

19Controversies in the Foundations of Analysis: Comments on Schubring’s ConflictsFoundations of Science 22 (1): 125140. 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

19Linearization of definable order relationsAnnals of Pure and Applied Logic 102 (12): 69100. 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 biSouslin partial orders and realordinal 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

18A definable E 0 class containing no definable elementsArchive for Mathematical Logic 54 (56): 711723. 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

17Gregory’s Sixth OperationFoundations of Science 23 (1): 133144. 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

17Cauchy’s Infinitesimals, His Sum Theorem, and Foundational ParadigmsFoundations of Science 23 (2): 267296. 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.

15Ulm Classification of Analytic Equivalence Relations in Generic UniversesMathematical Logic Quarterly 44 (3): 287303. 1998.

15Leibniz versus Ishiguro: Closing a Quarter Century of SyncategoremaniaHopos: The Journal of the International Society for the History of Philosophy of Science 6 (1): 117147. 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

15On Baire Measurable Homomorphisms of Quotients of the Additive Group of the RealsMathematical Logic Quarterly 46 (3): 377384. 2000.The quotient ℝ/G of the additive group of the reals modulo a countable subgroup G does not admit nontrivial Baire measurable automorphisms

14Special Model Axiom in Nonstandard Set TheoryMathematical Logic Quarterly 45 (3): 371384. 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 ksaturated model of PA for a given cardinal k

13A nonstandard set theory in the [mathematical formula]languageArchive for Mathematical Logic 39 (6): 403416. 2000.

13Counterexamples to countablesection Π21 uniformization and Π31 separationAnnals of Pure and Applied Logic 167 (3): 262283. 2016.

12DefinableE0classes at arbitrary projective levelsAnnals of Pure and Applied Logic 169 (9): 851871. 2018.
Areas of Interest
17th/18th Century Philosophy 