Beyond First Order Logic: from Number of Structures to Structure of Numbers Part Ii
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The Seven Virtues of Simple Type Theory
The Seven Virtues of Simple Type Theory William M. Farmer∗ McMaster University 26 November 2006 Abstract Simple type theory, also known as higher-order logic, is a natural ex- tension of first-order logic which is simple, elegant, highly expressive, and practical. This paper surveys the virtues of simple type theory and attempts to show that simple type theory is an attractive alterna- tive to first-order logic for practical-minded scientists, engineers, and mathematicians. It recommends that simple type theory be incorpo- rated into introductory logic courses offered by mathematics depart- ments and into the undergraduate curricula for computer science and software engineering students. 1 Introduction Mathematicians are committed to rigorous reasoning, but they usually shy away from formal logic. However, when mathematicians really need a for- mal logic—e.g., to teach their students the rules of quantification, to pin down exactly what a “property” is, or to formalize set theory—they almost invariably choose some form of first-order logic. Taking the lead of mathe- maticians, scientists and engineers usually choose first-order logic whenever they need a formal logic to express mathematical models precisely or to study the logical consequences of theories and specifications carefully. In science and engineering as well as in mathematics, first-order logic reigns supreme! A formal logic can be a theoretical tool for studying rigorous reasoning and a practical tool for performing rigorous reasoning. Today mathemati- cians sometimes use formal logics as theoretical tools, but they very rarely ∗ Address: Department of Computing and Software, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada. -
⊥N AS an ABSTRACT ELEMENTARY CLASS We Show
⊥N AS AN ABSTRACT ELEMENTARY CLASS JOHN T. BALDWIN, PAUL C. EKLOF, AND JAN TRLIFAJ We show that the concept of an Abstract Elementary Class (AEC) provides a unifying notion for several properties of classes of modules and discuss the stability class of these AEC. An abstract elementary class consists of a class of models K and a strengthening of the notion of submodel ≺K such that (K, ≺K) satisfies ⊥ the properties described below. Here we deal with various classes ( N, ≺N ); the precise definition of the class of modules ⊥N is given below. A key innovation is ⊥ that A≺N B means A ⊆ B and B/A ∈ N. We define in the text the main notions used here; important background defini- tions and proofs from the theory of modules can be found in [EM02] and [GT06]; concepts of AEC are due to Shelah (e.g. [She87]) but collected in [Bal]. The surprising fact is that some of the basic model theoretic properties of the ⊥ ⊥ class ( N, ≺N ) translate directly to algebraic properties of the class N and the module N over the ring R that have previously been studied in quite a different context (approximation theory of modules, infinite dimensional tilting theory etc.). Our main results, stated with increasingly strong conditions on the ring R, are: ⊥ Theorem 0.1. (1) Let R be any ring and N an R–module. If ( N, ≺N ) is an AEC then N is a cotorsion module. Conversely, if N is pure–injective, ⊥ then the class ( N, ≺N ) is an AEC. (2) Let R be a right noetherian ring and N be an R–module of injective di- ⊥ ⊥ mension ≤ 1. -
Constructive Models of Uncountably Categorical Theories
PROCEEDINGS OF THE AMERICAN MATHEMATICAL SOCIETY Volume 127, Number 12, Pages 3711{3719 S 0002-9939(99)04920-5 Article electronically published on May 6, 1999 CONSTRUCTIVE MODELS OF UNCOUNTABLY CATEGORICAL THEORIES BERNHARD HERWIG, STEFFEN LEMPP, AND MARTIN ZIEGLER (Communicated by Carl G. Jockusch, Jr.) Abstract. We construct a strongly minimal (and thus uncountably categori- cal) but not totally categorical theory in a finite language of binary predicates whose only constructive (or recursive) model is the prime model. 0. Introduction Effective (or recursive) model theory studies the degree to which constructions in model theory and algebra can be made effective. A presentation of a count- able model is an isomorphic copy with universe N = !.Aneffective (or computable,orMrecursive) presentation isN one where all the relations, functions, and constants on are given by uniformly computable functions. Now, for a count- able model N of a first-order theory T , there are various degrees to which the constructionM of can be made effective: We call the model constructive (or recursive,orcomputableM ) if it has an effective presentation, orM equivalently if its open diagram (i.e., the collection of all quantifier-free sentences true in ( ;a)a M (in some presentation) is computable (or recursive)). We call the modelM decid-∈ able if its elementary diagram (i.e., the collection of all first-order sentencesM true in ( ;a)a M,insome presentation) is decidable (i.e., computable). Obviously, anyM decidable∈ model is constructive, but the converse fails. In fact, the study of constructive models is much harder than the study of decidable models since, in the former case, much less is known about the first-order theory. -
Arxiv:1604.07743V3 [Math.LO] 14 Apr 2017 Aeoiiy Nicrils Re Property
SATURATION AND SOLVABILITY IN ABSTRACT ELEMENTARY CLASSES WITH AMALGAMATION SEBASTIEN VASEY Abstract. Theorem 0.1. Let K be an abstract elementary class (AEC) with amalga- mation and no maximal models. Let λ> LS(K). If K is categorical in λ, then the model of cardinality λ is Galois-saturated. This answers a question asked independently by Baldwin and Shelah. We deduce several corollaries: K has a unique limit model in each cardinal below λ, (when λ is big-enough) K is weakly tame below λ, and the thresholds of several existing categoricity transfers can be improved. We also prove a downward transfer of solvability (a version of superstability introduced by Shelah): Corollary 0.2. Let K be an AEC with amalgamation and no maximal mod- els. Let λ>µ> LS(K). If K is solvable in λ, then K is solvable in µ. Contents 1. Introduction 1 2. Extracting strict indiscernibles 4 3. Solvability and failure of the order property 8 4. Solvability and saturation 10 5. Applications 12 References 18 arXiv:1604.07743v3 [math.LO] 14 Apr 2017 1. Introduction 1.1. Motivation. Morley’s categoricity theorem [Mor65] states that if a countable theory has a unique model of some uncountable cardinality, then it has a unique model in all uncountable cardinalities. The method of proof led to the development of stability theory, now a central area of model theory. In the mid seventies, Shelah L conjectured a similar statement for classes of models of an ω1,ω-theory [She90, Date: September 7, 2018 AMS 2010 Subject Classification: Primary 03C48. -
Elementary Model Theory Notes for MATH 762
George F. McNulty Elementary Model Theory Notes for MATH 762 drawings by the author University of South Carolina Fall 2011 Model Theory MATH 762 Fall 2011 TTh 12:30p.m.–1:45 p.m. in LeConte 303B Office Hours: 2:00pm to 3:30 pm Monday through Thursday Instructor: George F. McNulty Recommended Text: Introduction to Model Theory By Philipp Rothmaler What We Will Cover After a couple of weeks to introduce the fundamental concepts and set the context (material chosen from the first three chapters of the text), the course will proceed with the development of first-order model theory. In the text this is the material covered beginning in Chapter 4. Our aim is cover most of the material in the text (although not all the examples) as well as some material that extends beyond the topics covered in the text (notably a proof of Morley’s Categoricity Theorem). The Work Once the introductory phase of the course is completed, there will be a series of problem sets to entertain and challenge each student. Mastering the problem sets should give each student a detailed familiarity with the main concepts and theorems of model theory and how these concepts and theorems might be applied. So working through the problems sets is really the heart of the course. Most of the problems require some reflection and can usually not be resolved in just one sitting. Grades The grades in this course will be based on each student’s work on the problem sets. Roughly speaking, an A will be assigned to students whose problems sets eventually reveal a mastery of the central concepts and theorems of model theory; a B will be assigned to students whose work reveals a grasp of the basic concepts and a reasonable competence, short of mastery, in putting this grasp into play to solve problems. -
An Outline of Algebraic Set Theory
An Outline of Algebraic Set Theory Steve Awodey Dedicated to Saunders Mac Lane, 1909–2005 Abstract This survey article is intended to introduce the reader to the field of Algebraic Set Theory, in which models of set theory of a new and fascinating kind are determined algebraically. The method is quite robust, admitting adjustment in several respects to model different theories including classical, intuitionistic, bounded, and predicative ones. Under this scheme some familiar set theoretic properties are related to algebraic ones, like freeness, while others result from logical constraints, like definability. The overall theory is complete in two important respects: conventional elementary set theory axiomatizes the class of algebraic models, and the axioms provided for the abstract algebraic framework itself are also complete with respect to a range of natural models consisting of “ideals” of sets, suitably defined. Some previous results involving realizability, forcing, and sheaf models are subsumed, and the prospects for further such unification seem bright. 1 Contents 1 Introduction 3 2 The category of classes 10 2.1 Smallmaps ............................ 12 2.2 Powerclasses............................ 14 2.3 UniversesandInfinity . 15 2.4 Classcategories .......................... 16 2.5 Thetoposofsets ......................... 17 3 Algebraic models of set theory 18 3.1 ThesettheoryBIST ....................... 18 3.2 Algebraic soundness of BIST . 20 3.3 Algebraic completeness of BIST . 21 4 Classes as ideals of sets 23 4.1 Smallmapsandideals . .. .. 24 4.2 Powerclasses and universes . 26 4.3 Conservativity........................... 29 5 Ideal models 29 5.1 Freealgebras ........................... 29 5.2 Collection ............................. 30 5.3 Idealcompleteness . .. .. 32 6 Variations 33 References 36 2 1 Introduction Algebraic set theory (AST) is a new approach to the construction of models of set theory, invented by Andr´eJoyal and Ieke Moerdijk and first presented in [16]. -
Self-Similarity in the Foundations
Self-similarity in the Foundations Paul K. Gorbow Thesis submitted for the degree of Ph.D. in Logic, defended on June 14, 2018. Supervisors: Ali Enayat (primary) Peter LeFanu Lumsdaine (secondary) Zachiri McKenzie (secondary) University of Gothenburg Department of Philosophy, Linguistics, and Theory of Science Box 200, 405 30 GOTEBORG,¨ Sweden arXiv:1806.11310v1 [math.LO] 29 Jun 2018 2 Contents 1 Introduction 5 1.1 Introductiontoageneralaudience . ..... 5 1.2 Introduction for logicians . .. 7 2 Tour of the theories considered 11 2.1 PowerKripke-Plateksettheory . .... 11 2.2 Stratifiedsettheory ................................ .. 13 2.3 Categorical semantics and algebraic set theory . ....... 17 3 Motivation 19 3.1 Motivation behind research on embeddings between models of set theory. 19 3.2 Motivation behind stratified algebraic set theory . ...... 20 4 Logic, set theory and non-standard models 23 4.1 Basiclogicandmodeltheory ............................ 23 4.2 Ordertheoryandcategorytheory. ...... 26 4.3 PowerKripke-Plateksettheory . .... 28 4.4 First-order logic and partial satisfaction relations internal to KPP ........ 32 4.5 Zermelo-Fraenkel set theory and G¨odel-Bernays class theory............ 36 4.6 Non-standardmodelsofsettheory . ..... 38 5 Embeddings between models of set theory 47 5.1 Iterated ultrapowers with special self-embeddings . ......... 47 5.2 Embeddingsbetweenmodelsofsettheory . ..... 57 5.3 Characterizations.................................. .. 66 6 Stratified set theory and categorical semantics 73 6.1 Stratifiedsettheoryandclasstheory . ...... 73 6.2 Categoricalsemantics ............................... .. 77 7 Stratified algebraic set theory 85 7.1 Stratifiedcategoriesofclasses . ..... 85 7.2 Interpretation of the Set-theories in the Cat-theories ................ 90 7.3 ThesubtoposofstronglyCantorianobjects . ....... 99 8 Where to go from here? 103 8.1 Category theoretic approach to embeddings between models of settheory . -
More Model Theory Notes Miscellaneous Information, Loosely Organized
More Model Theory Notes Miscellaneous information, loosely organized. 1. Kinds of Models A countable homogeneous model M is one such that, for any partial elementary map f : A ! M with A ⊆ M finite, and any a 2 M, f extends to a partial elementary map A [ fag ! M. As a consequence, any partial elementary map to M is extendible to an automorphism of M. Atomic models (see below) are homogeneous. A prime model of T is one that elementarily embeds into every other model of T of the same cardinality. Any theory with fewer than continuum-many types has a prime model, and if a theory has a prime model, it is unique up to isomorphism. Prime models are homogeneous. On the other end, a model is universal if every other model of its size elementarily embeds into it. Recall a type is a set of formulas with the same tuple of free variables; generally to be called a type we require consistency. The type of an element or tuple from a model is all the formulas it satisfies. One might think of the type of an element as a sort of identity card for automorphisms: automorphisms of a model preserve types. A complete type is the analogue of a complete theory, one where every formula of the appropriate free variables or its negation appears. Types of elements and tuples are always complete. A type is principal if there is one formula in the type that implies all the rest; principal complete types are often called isolated. A trivial example of an isolated type is that generated by the formula x = c where c is any constant in the language, or x = t(¯c) where t is any composition of appropriate-arity functions andc ¯ is a tuple of constants. -
Structural Logic and Abstract Elementary Classes with Intersections
STRUCTURAL LOGIC AND ABSTRACT ELEMENTARY CLASSES WITH INTERSECTIONS WILL BONEY AND SEBASTIEN VASEY Abstract. We give a syntactic characterization of abstract elementary classes (AECs) closed under intersections using a new logic with a quantifier for iso- morphism types that we call structural logic: we prove that AECs with in- tersections correspond to classes of models of a universal theory in structural logic. This generalizes Tarski's syntactic characterization of universal classes. As a corollary, we obtain that any AEC closed under intersections with count- able L¨owenheim-Skolem number is axiomatizable in L1;!(Q), where Q is the quantifier \there exists uncountably many". Contents 1. Introduction 1 2. Structural quantifiers 3 3. Axiomatizing abstract elementary classes with intersections 7 4. Equivalence vs. Axiomatization 11 References 13 1. Introduction 1.1. Background and motivation. Shelah's abstract elementary classes (AECs) [She87,Bal09,She09a,She09b] are a semantic framework to study the model theory of classes that are not necessarily axiomatized by an L!;!-theory. Roughly speak- ing (see Definition 2.4), an AEC is a pair (K; ≤K) satisfying some of the category- theoretic properties of (Mod(T ); ), for T an L!;!-theory. This encompasses classes of models of an L1;! sentence (i.e. infinite conjunctions and disjunctions are al- lowed), and even L1;!(hQλi ii<α) theories, where Qλi is the quantifier \there exists λi-many". Since the axioms of AECs do not contain any axiomatizability requirement, it is not clear whether there is a natural logic whose class of models are exactly AECs. More precisely, one can ask whether there is a natural abstract logic (in the sense of Barwise, see the survey [BFB85]) so that classes of models of theories in that logic are AECs and any AEC is axiomatized by a theory in that logic. -
On Categorical Theory-Building: Beyond the Formal
Andrei Rodin (Ecole Normale Superieure) On Categorical Theory-Building: Beyond the Formal 1. Introduction: Languages, Foundations and Reification of Concepts The term "language" is colloquially used in mathematics to refer to a theory, which grasps common features of a large range (or even all) of other mathematical theories and so can serve as a unifying conceptual framework for these theories. "Set- theoretic language" is a case in point. The systematic work of translation of the whole of mathematics into the set-theoretic language has been endeavoured in 20-th century by a group of mathematicians under the collective name of Nicolas Bourbaki. Bourbakist mathematics proved successful both in research and higher education (albeit not in the school math education) and is practiced until today at mathematical departments worldwide. The project of Bourbaki as well as other attempts to do mathematics "set- theoretically" should be definitely distinguished from the project of reduction of mathematics to set theory defended by Quine and some other philosophers. This latter project is based on the claim that all true mathematical propositions are deducible from axioms of Zermelo-Frenkael set theory with Choice (ZFC) or another appropriate system of axioms for sets, so basically all the mathematics is set theory. A working mathematician usually sees this claim as an example of philosophical absurdity on a par with Zeno's claim that there is no motion, and Bourbaki never tried to put it forward. Actually Bourbaki used set theory (more precisely their own version of axiomatic theory of sets) for doing mathematics in very much the same way in which classical first-order logic is used for doing axiomatic theories like ZFC. -
Mathematics and the Brain: a Category Theoretical Approach to Go Beyond the Neural Correlates of Consciousness
entropy Review Mathematics and the Brain: A Category Theoretical Approach to Go Beyond the Neural Correlates of Consciousness 1,2,3, , 4,5,6,7, 8, Georg Northoff * y, Naotsugu Tsuchiya y and Hayato Saigo y 1 Mental Health Centre, Zhejiang University School of Medicine, Hangzhou 310058, China 2 Institute of Mental Health Research, University of Ottawa, Ottawa, ON K1Z 7K4 Canada 3 Centre for Cognition and Brain Disorders, Hangzhou Normal University, Hangzhou 310036, China 4 School of Psychological Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria 3800, Australia; [email protected] 5 Turner Institute for Brain and Mental Health, Monash University, Melbourne, Victoria 3800, Australia 6 Advanced Telecommunication Research, Soraku-gun, Kyoto 619-0288, Japan 7 Center for Information and Neural Networks (CiNet), National Institute of Information and Communications Technology (NICT), Suita, Osaka 565-0871, Japan 8 Nagahama Institute of Bio-Science and Technology, Nagahama 526-0829, Japan; [email protected] * Correspondence: georg.northoff@theroyal.ca All authors contributed equally to the paper as it was a conjoint and equally distributed work between all y three authors. Received: 18 July 2019; Accepted: 9 October 2019; Published: 17 December 2019 Abstract: Consciousness is a central issue in neuroscience, however, we still lack a formal framework that can address the nature of the relationship between consciousness and its physical substrates. In this review, we provide a novel mathematical framework of category theory (CT), in which we can define and study the sameness between different domains of phenomena such as consciousness and its neural substrates. CT was designed and developed to deal with the relationships between various domains of phenomena. -
Totally Categorical Structures
TRANSACTIONSof the AMERICANMATHEMATICAL SOCIETY Volume 313, Number 1, May 1989 TOTALLY CATEGORICAL STRUCTURES EHUD HRUSHOVSKJ Abstract. A first order theory is totally categorical if it has exactly one model in each infinite power. We prove here that every such theory admits a finite language, and is finitely axiomatizable in that language, modulo axioms stating that the structure is infinite. This was conjectured by Vaught. We also show that every N0-stable, N0-categorical structure is a reduct of one that has finitely many models in small uncountable powers. In the case of structures of disintegrated type we nearly find an explicit structure theorem, and show that the remaining obstacle resides in certain nilpotent automorphism groups. 1. Introduction A sequence of fundamental papers in model theory has given rise to an un- derstanding of the totally categorical structures as those structures that are co- ordinatized (in a certain precise way) by a projective space over a finite field (or in the degenerate case by a pure set). Much of this work was motivated by a conjecture of Vaught: a totally categorical theory can be axiomatized by a finite set of sentences that has arbitrarily large finite models, together with axioms stating that the intended models are infinite. The part stating that every finite set of axioms does have a finite model was settled in [Z] and refined in [CHL]. §2 of the present paper proves the conjecture in full. In particular, it follows that the class of totally categorical theories is countable. In [CHL], the context of research was shifted from totally categorical the- ories to N0-categorical, N0-stable ones; those theories whose models are coor- dinatized by a collection of projective spaces over finite fields and degenerate spaces (rather than just one).