
6Definable minimal collapse functions at arbitrary projective levelsJournal of Symbolic Logic 84 (1): 266289. 2019.

9Minimal axiomatic frameworks for definable hyperreals with transferJournal of Symbolic Logic 83 (1): 385391. 2018.

9DefinableE0classes at arbitrary projective levelsAnnals of Pure and Applied Logic 169 (9): 851871. 2018.

7Countable OD sets of reals belong to the ground modelArchive for Mathematical Logic 57 (34): 285298. 2018.It is true in the Cohen, Solovayrandom, dominaning, and Sacks generic extension, that every countable ordinaldefinable set of reals belongs to the ground universe. It is true in the Solovay collapse model that every nonempty OD countable set of sets of reals consists of \ elements.

13Cauchy’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.

4A GroszekLaver pair of undistinguishable E0classesMathematical Logic Quarterly 63 (12): 1931. 2017.

14Gregory’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

148What 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.

3A 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.

19A 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

29Uniqueness, 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

1Internal Approach to External Sets and Universes: Part 1. Bounded Set TheoryStudia Logica 55 (2): 229257. 1995.A problem which enthusiasts of IST, Nelson's internal set theory, usually face is how to treat external sets in the internal universe which does not contain them directly. To solve this problem, we consider BST, bounded set theory, a modification of IST which is, briefly, a theory for the family of those IST sets which are members of standard sets. We show that BST is strong enough to incorporate external sets in the internal universe in a way sufficient to develop the most advanced applications…Read more

32An 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

153Is 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

19Proofs 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

9Loeb Measure from the Point of View of a Coin Flipping GameMathematical Logic Quarterly 42 (1): 1926. 1996.A hyperfinitely long coin flipping game between the Gambler and the Casino, associated with a given set A, is considered. It turns out that the Gambler has a winning strategy if and only if A has Loeb measure 0. The Casino has a winning strategy if and only if A contains an internal subset of positive Loeb measure

30Elementary 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

39A 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

16Controversies 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

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

29On 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

57Internal 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.

An 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 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.

7A definable E 0 class containing no definable elementsArchive for Mathematical Logic 54 (56): 711723. 2015.

11Special 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

5Linearization 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

25Extending 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.
Areas of Interest
17th/18th Century Philosophy 