Stability Theory, Permutations of Indiscernibles, and Embedded Finite Models
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Order Types and Structure of Orders
ORDER TYPES AND STRUCTURE OF ORDERS BY ANDRE GLEYZALp) 1. Introduction. This paper is concerned with operations on order types or order properties a and the construction of order types related to a. The reference throughout is to simply or linearly ordered sets, and we shall speak of a as either property or type. Let a and ß be any two order types. An order A will be said to be of type aß if it is the sum of /3-orders (orders of type ß) over an a-order; i.e., if A permits of decomposition into nonoverlapping seg- ments each of order type ß, the segments themselves forming an order of type a. We have thus associated with every pair of order types a and ß the product order type aß. The definition of product for order types automatically associates with every order type a the order types aa = a2, aa2 = a3, ■ ■ ■ . We may further- more define, for all ordinals X, a Xth power of a, a\ and finally a limit order type a1. This order type has certain interesting properties. It has closure with respect to the product operation, for the sum of ar-orders over an a7-order is an a'-order, i.e., a'al = aI. For this reason we call a1 iterative. In general, we term an order type ß having the property that ßß = ß iterative, a1 has the following postulational identification: 1. a7 is a supertype of a; that is to say, all a-orders are a7-orders. 2. a1 is iterative. -
Stability Theory
Department of Mathematics Master's thesis Stability Theory Author: Supervisor: Sven Bosman Dr. Jaap van Oosten Second reader: Prof. Dr. Gunther Cornelissen May 15, 2018 Acknowledgements First and foremost, I would like to thank my supervisor, Dr. Jaap van Oosten, for guiding me. He gave me a chance to pursue my own interests for this project, rather then picking a topic which would have been much easier to supervise. He has shown great patience when we were trying to determine how to get a grip on this material, and has made many helpful suggestions and remarks during the process. I would like to thank Prof. Dr. Gunther Cornelissen for being the second reader of this thesis. I would like to thank Dr. Alex Kruckman for his excellent answer to my question on math.stackexchange.com. He helped me with a problem I had been stuck with for quite some time. I have really enjoyed the master's thesis logic seminar the past year, and would like to thank the participants Tom, Menno, Jetze, Mark, Tim, Bart, Feike, Anton and Mireia for listening to my talks, no matter how boring they might have been at times. Special thanks go to Jetze Zoethout for reading my entire thesis and providing me with an extraordinary number of helpful tips, comments, suggestions, corrections and improvements. Most of my thesis was written in the beautiful library of the Utrecht University math- ematics department, which has been my home away from home for the last three years. I would like to thank all my friends there for the many enjoyable lunchbreaks, the interesting political discussions, and the many, many jokes. -
Arxiv:1801.06566V1 [Math.LO] 19 Jan 2018
MODEL THEORY AND MACHINE LEARNING HUNTER CHASE AND JAMES FREITAG ABSTRACT. About 25 years ago, it came to light that a single combinatorial property deter- mines both an important dividing line in model theory (NIP) and machine learning (PAC- learnability). The following years saw a fruitful exchange of ideas between PAC learning and the model theory of NIP structures. In this article, we point out a new and similar connection between model theory and machine learning, this time developing a correspon- dence between stability and learnability in various settings of online learning. In particular, this gives many new examples of mathematically interesting classes which are learnable in the online setting. 1. INTRODUCTION The purpose of this note is to describe the connections between several notions of com- putational learning theory and model theory. The connection between probably approxi- mately correct (PAC) learning and the non-independence property (NIP) is well-known and was originally noticed by Laskowski [8]. In the ensuing years, there have been numerous interactions between the combinatorics associated with PAC learning and model theory in the NIP setting. Below, we provide a quick introduction to the PAC-learning setting as well as learning in general. Our main purpose, however, is to explain a new connection between the model theory and machine learning. Roughly speaking, our manuscript is similar to [8], but develops the connection between stability and online learning. That the combinatorial quantity of VC-dimension plays an essential role in isolating the main dividing line in both PAC-learning and perhaps the second most prominent dividing line in model-theoretic classification theory (NIP/IP) is a remarkable fact. -
Arxiv:1609.03252V6 [Math.LO] 21 May 2018 M 00Sbetcasfiain Rmr 34.Secondary: 03C48
TOWARD A STABILITY THEORY OF TAME ABSTRACT ELEMENTARY CLASSES SEBASTIEN VASEY Abstract. We initiate a systematic investigation of the abstract elementary classes that have amalgamation, satisfy tameness (a locality property for or- bital types), and are stable (in terms of the number of orbital types) in some cardinal. Assuming the singular cardinal hypothesis (SCH), we prove a full characterization of the (high-enough) stability cardinals, and connect the sta- bility spectrum with the behavior of saturated models. We deduce (in ZFC) that if a class is stable on a tail of cardinals, then it has no long splitting chains (the converse is known). This indicates that there is a clear notion of superstability in this framework. We also present an application to homogeneous model theory: for D a homogeneous diagram in a first-order theory T , if D is both stable in |T | and categorical in |T | then D is stable in all λ ≥|T |. Contents 1. Introduction 2 2. Preliminaries 4 3. Continuity of forking 8 4. ThestabilityspectrumoftameAECs 10 5. The saturation spectrum 15 6. Characterizations of stability 18 7. Indiscernibles and bounded equivalence relations 20 arXiv:1609.03252v6 [math.LO] 21 May 2018 8. Strong splitting 22 9. Dividing 23 10. Strong splitting in stable tame AECs 25 11. Stability theory assuming continuity of splitting 27 12. Applications to existence and homogeneous model theory 31 References 32 Date: September 7, 2018 AMS 2010 Subject Classification: Primary 03C48. Secondary: 03C45, 03C52, 03C55, 03C75, 03E55. Key words and phrases. Abstract elementary classes; Tameness; Stability spectrum; Saturation spectrum; Limit models. 1 2 SEBASTIEN VASEY 1. -
Measures in Model Theory
Measures in model theory Anand Pillay University of Leeds Logic and Set Theory, Chennai, August 2010 IntroductionI I I will discuss the growing use and role of measures in \pure" model theory, with an emphasis on extensions of stability theory outside the realm of stable theories. I The talk is related to current work with Ehud Hrushovski and Pierre Simon (building on earlier work with Hrushovski and Peterzil). I I will be concerned mainly, but not exclusively, with \tame" rather than \foundational" first order theories. I T will denote a complete first order theory, 1-sorted for convenience, in language L. I There are canonical objects attached to T such as Bn(T ), the Boolean algebra of formulas in free variables x1; ::; xn up to equivalence modulo T , and the type spaces Sn(T ) of complete n-types (ultrafilters on Bn(T )). IntroductionII I Everything I say could be expressed in terms of the category of type spaces (including SI (T ) for I an infinite index set). I However it has become standard to work in a fixed saturated model M¯ of T , and to study the category Def(M¯ ) of sets X ⊆ M¯ n definable, possibly with parameters, in M¯ , as well as solution sets X of types p 2 Sn(A) over small sets A of parameters. I Let us remark that the structure (C; +; ·) is a saturated model of ACF0, but (R; +; ·) is not a saturated model of RCF . I The subtext is the attempt to find a meaningful classification of first order theories. Stable theoriesI I The stable theories are the \logically perfect" theories (to coin a phrase of Zilber). -
Multiplication in Vector Lattices
MULTIPLICATION IN VECTOR LATTICES NORMAN M. RICE 1. Introduction. B. Z. Vulih has shown (13) how an essentially unique intrinsic multiplication can be defined in a Dedekind complete vector lattice L having a weak order unit. Since this work is available only in Russian, a brief outline is given in § 2 (cf. also the review by E. Hewitt (4), and for details, consult (13) or (11)). In general, not every pair of elements in L will have a product in L. In § 3 we discuss certain properties which ensure that, in fact, the multiplication will be universally defined, and it turns out that L can always be embedded as an order-dense order ideal in a larger space L# which has these properties. It is then possible to define multiplication in spaces without a unit. In § 4 we show that if L has a normal integral 0, then 4> can be extended to a normal integral on a larger space Li(<t>) in L#, and £i(0) may be regarded as an abstract integral space. In § 5 a very general form of the Radon-Niko- dym theorem is proved, and in § 6 this is used to give a relatively simple proof of a theorem of Segal giving a necessary and sufficient condition for the Radon-Nikodym theorem to hold in a measure space. 2. Multiplication in spaces with a unit. Let L be a vector lattice which is Dedekind complete (i.e., every set which is bounded above has a least upper bound) and has a weak order unit 1 (i.e., inf (1, x) > 0, whenever x > 0). -
Notes on Totally Categorical Theories
Notes on totally categorical theories Martin Ziegler 1991 0 Introduction Cherlin, Harrington and Lachlan’s paper on ω0-categorical, ω0-stable theories ([CHL]) was the starting point of geometrical stability theory. The progress made since then allows us better to understand what they did in modern terms (see [PI]) and also to push the description of totally categorical theories further, (see [HR1, AZ1, AZ2]). The first two sections of what follows give an exposition of the results of [CHL]. Then I explain how a totally categorical theory can be decomposed by a sequence of covers and in the last section I discuss the problem how covers can look like. I thank the parisian stabilists for their invation to lecture on these matters, and also for their help during the talks. 1 Fundamental Properties Let T be a totally categorical theory (i.e. T is a complete countable theory, without finite models which is categorical in all infinite cardinalities). Since T is ω1-categorical we know that a) T has finite Morley-rank, which coincides with the Lascar rank U. b) T is unidimensional : All non-algebraic types are non-orthogonal. The main result of [CHL] is that c) T is locally modular. A pregeometry X (i.e. a matroid) is modular if two subspaces are always independent over their intersection. X is called locally modular if two subspaces are independent over their intersection provided this intersection has positive dimension. A pregeometry is a geometry if the closure of the empty set is empty and the one-dimensional subspaces are singletons. -
Model Theory, Stability Theory, and the Free Group
Model theory, stability theory, and the free group Anand Pillay Lecture notes for the workshop on Geometric Group Theory and Logic at the University of Illinois at Chicago, August 2011 1 Overview Overview • I will take as a definition of model theory the study (classification?) of first order theories T . • A \characteristic" invariant of a first order theory T is its category Def(T ) of definable sets. Another invariant is the category Mod(T ) of models of T . • Often Def(T ) is a familiar category in mathematics. For example when T = ACF0, Def(T ) is essentially the category of complex algebraic vari- eties defined over Q. • Among first order theories the \perfect" ones are the stable theories. • Stability theory provides a number of tools, notions, concepts, for under- standing the category Def(T ) for a stable theory T . • Among stable theories are the theory of algebraically closed fields, the theory of differentially closed fields, as well as the theory of abelian groups (in the group language). • An ingenious method, \Hrushovski constructions", originally developed to yield counterexamples to a conjecture of Zilber, produces new stable theories with surprising properties. • However, modulo the work of Sela, nature has provided us with another complex and fascinating stable first order theory, the theory Tfg of the noncommutative free group. • One can argue that the true \algebraic geometry over the free group" should be the study of Def(Tfg). 1 • Some references are given at the end of the notes. The references (1), (2) include all the material covered in the first section of these notes (and much more). -
When Is a Lots Densely Orderable?
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Topology and its Applications 30 (1988) 225-235 225 North-Holland WHEN IS A LOTS DENSELY ORDERABLE? Victor NEUMANN-LARA Institute de Matetmiticas, Uniuersidad National Autdnoma de M&ico, Ciudad Universitaria, Mhico 20, D.F. Richard C. WILSON Departamento de Matemdticas, Universidad Autdnoma Metropolitana, Unidad Iztapalapa, M&ico 13, D.F. Received 15 May 1986 Revised 19 October 1987 We obtain sufficient conditions for a linearly ordered topological space (LOTS) to be densely orderable. As a consequence we obtain a characterization of those metrizable LOTS with connected ordered compactifications. AMS (MOS) Subj. Class.: Primary 54F05 1. Introduction A well-known result states that the weight w of a linearly ordered topological space (LOTS) is equal to the sum of the density d and the number of jumps j. Thus if j > d, then w =j and hence j is an order-topological invariant of the space in the sense that any other order which induces the same topology will have the same number of jumps. On the other hand, if j G d (in particular if j = Ko) then this is not necessarily the case-for example, the space of rationals Q with the order topology is homeomophic to Q x (0, l} with the lexicographic order topology. In this paper we will obtain conditions under which a LOTS can be reordered without jumps, that is to say under which there exists a dense order inducing the same topology. 2. -
A Survey on Tame Abstract Elementary Classes
A SURVEY ON TAME ABSTRACT ELEMENTARY CLASSES WILL BONEY AND SEBASTIEN VASEY Abstract. Tame abstract elementary classes are a broad nonele- mentary framework for model theory that encompasses several ex- amples of interest. In recent years, progress toward developing a classification theory for them has been made. Abstract indepen- dence relations such as Shelah's good frames have been found to be key objects. Several new categoricity transfers have been obtained. We survey these developments using the following result (due to the second author) as our guiding thread: Theorem. If a universal class is categorical in cardinals of arbi- trarily high cofinality, then it is categorical on a tail of cardinals. Contents 1. Introduction 2 2. A primer in abstract elementary classes without tameness 8 3. Tameness: what and where 24 4. Categoricity transfer in universal classes: an overview 36 5. Independence, stability, and categoricity in tame AECs 44 6. Conclusion 68 7. Historical remarks 71 References 79 Date: July 22, 2016. This material is based upon work done while the first author was supported by the National Science Foundation under Grant No. DMS-1402191. This material is based upon work done while the second author was supported by the Swiss National Science Foundation under Grant No. 155136. 1 2 WILL BONEY AND SEBASTIEN VASEY 1. Introduction Abstract elementary classes (AECs) are a general framework for nonele- mentary model theory. They encompass many examples of interest while still allowing some classification theory, as exemplified by Shelah's recent two-volume book [She09b, She09c] titled Classification Theory for Abstract Elementary Classes. -
General-Well-Ordered Sets
J. Austral. Math. Soc. 19 (Series A), (1975), 7-20. GENERAL-WELL-ORDERED SETS J. L. HICKMAN (Received 10 April 1972) Communicated by J. N. Crossley It is of course well known that within the framework of any reasonable set theory whose axioms include that of choice, we can characterize well-orderings in two different ways: (1) a total order for which every nonempty subset has a minimal element; (2) a total order in which there are no infinite descending chains. Now the theory of well-ordered sets and their ordinals that is expounded in various texts takes as its definition characterization (1) above; in this paper we commence an investigation into the corresponding theory that takes character- ization (2) as its starting point. Naturally if we are to obtain any differences at all, we must exclude the axiom of choice from our set theory. Thus we state right at the outset that we are working in Zermelo-Fraenkel set theory without choice. This is not enough, however, for it may turn out that the axiom of choice is not really necessary for the equivalence of (1) and (2), and if this were so, we would still not obtain any deviation from the "classical" theory. Thus the first section of this paper will be devoted to showing that we can in fact have sets that are well-ordered according to (2) but not according to (1). Naturally we have no hope of reversing this situation, for it is a ZF-theorem that any set well-ordered by (1) is also well-ordered by (2). -
Logic and Rational Languages of Words Indexed by Linear Orderings
Logic and Rational Languages of Words Indexed by Linear Orderings Nicolas Bedon1, Alexis B`es2, Olivier Carton3, and Chlo´eRispal1 1 Universit´eParis-Est and CNRS Laboratoire d’informatique de l’Institut Gaspard Monge, CNRS UMR 8049 Email: [email protected], [email protected] 2 Universit´eParis-Est, LACL Email: [email protected], 3 Universit´eParis 7 and CNRS LIAFA, CNRS UMR 7089 Email: [email protected] Abstract. We prove that every rational language of words indexed by linear orderings is definable in monadic second-order logic. We also show that the converse is true for the class of languages indexed by countable scattered linear orderings, but false in the general case. As a corollary we prove that the inclusion problem for rational languages of words indexed by countable linear orderings is decidable. 1 Introduction In [4, 6], Bruy`ere and Carton introduce automata and rational expressions for words on linear orderings. These notions unify naturally previously defined no- tions for finite words, left- and right-infinite words, bi-infinite words, and ordinal words. They also prove that a Kleene-like theorem holds when the orderings are restricted to countable scattered linear orderings; recall that a linear ordering is scattered if it does not contain any dense sub-ordering. Since [4], the study of automata on linear orderings was carried on in several papers. The emptiness problem and the inclusion problem for rational languages is addressed in [7, 11]. The papers [5, 2] provide a classification of rational languages with respect to the rational operations needed to describe them.