Borel Hierarchy and Omega Context Free Languages Olivier Finkel
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Calibrating Determinacy Strength in Levels of the Borel Hierarchy
CALIBRATING DETERMINACY STRENGTH IN LEVELS OF THE BOREL HIERARCHY SHERWOOD J. HACHTMAN Abstract. We analyze the set-theoretic strength of determinacy for levels of the Borel 0 hierarchy of the form Σ1+α+3, for α < !1. Well-known results of H. Friedman and D.A. Martin have shown this determinacy to require α+1 iterations of the Power Set Axiom, but we ask what additional ambient set theory is strictly necessary. To this end, we isolate a family of Π1-reflection principles, Π1-RAPα, whose consistency strength corresponds 0 CK exactly to that of Σ1+α+3-Determinacy, for α < !1 . This yields a characterization of the levels of L by or at which winning strategies in these games must be constructed. When α = 0, we have the following concise result: the least θ so that all winning strategies 0 in Σ4 games belong to Lθ+1 is the least so that Lθ j= \P(!) exists + all wellfounded trees are ranked". x1. Introduction. Given a set A ⊆ !! of sequences of natural numbers, consider a game, G(A), where two players, I and II, take turns picking elements of a sequence hx0; x1; x2;::: i of naturals. Player I wins the game if the sequence obtained belongs to A; otherwise, II wins. For a collection Γ of subsets of !!, Γ determinacy, which we abbreviate Γ-DET, is the statement that for every A 2 Γ, one of the players has a winning strategy in G(A). It is a much-studied phenomenon that Γ -DET has mathematical strength: the bigger the pointclass Γ, the stronger the theory required to prove Γ -DET. -
Topology and Descriptive Set Theory
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector TOPOLOGY AND ITS APPLICATIONS ELSEVIER Topology and its Applications 58 (1994) 195-222 Topology and descriptive set theory Alexander S. Kechris ’ Department of Mathematics, California Institute of Technology, Pasadena, CA 91125, USA Received 28 March 1994 Abstract This paper consists essentially of the text of a series of four lectures given by the author in the Summer Conference on General Topology and Applications, Amsterdam, August 1994. Instead of attempting to give a general survey of the interrelationships between the two subjects mentioned in the title, which would be an enormous and hopeless task, we chose to illustrate them in a specific context, that of the study of Bore1 actions of Polish groups and Bore1 equivalence relations. This is a rapidly growing area of research of much current interest, which has interesting connections not only with topology and set theory (which are emphasized here), but also to ergodic theory, group representations, operator algebras and logic (particularly model theory and recursion theory). There are four parts, corresponding roughly to each one of the lectures. The first contains a brief review of some fundamental facts from descriptive set theory. In the second we discuss Polish groups, and in the third the basic theory of their Bore1 actions. The last part concentrates on Bore1 equivalence relations. The exposition is essentially self-contained, but proofs, when included at all, are often given in the barest outline. Keywords: Polish spaces; Bore1 sets; Analytic sets; Polish groups; Bore1 actions; Bore1 equivalence relations 1. -
Abstract Determinacy in the Low Levels of The
ABSTRACT DETERMINACY IN THE LOW LEVELS OF THE PROJECTIVE HIERARCHY by Michael R. Cotton We give an expository introduction to determinacy for sets of reals. If we are to assume the Axiom of Choice, then not all sets of reals can be determined. So we instead establish determinacy for sets according to their levels in the usual hierarchies of complexity. At a certain point ZFC is no longer strong enough, and we must begin to assume large cardinals. The primary results of this paper are Martin's theorems that Borel sets are determined, homogeneously Suslin sets are determined, and if a measurable cardinal κ exists then the complements of analytic sets are κ-homogeneously Suslin. We provide the necessary preliminaries, prove Borel determinacy, introduce measurable cardinals and ultrapowers, and then prove analytic determinacy from the existence of a measurable cardinal. Finally, we give a very brief overview of some further results which provide higher levels of determinacy relative to larger cardinals. DETERMINACY IN THE LOW LEVELS OF THE PROJECTIVE HIERARCHY A Thesis Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Master of Arts Department of Mathematics by Michael R. Cotton Miami University Oxford, Ohio 2012 Advisor: Dr. Paul Larson Reader: Dr. Dennis K. Burke Reader: Dr. Tetsuya Ishiu Contents Introduction 1 0.1 Some notation and conventions . 2 1 Reals, trees, and determinacy 3 1.1 The reals as !! .............................. 3 1.2 Determinacy . 5 1.3 Borel sets . 8 1.4 Projective sets . 10 1.5 Tree representations . 12 2 Borel determinacy 14 2.1 Games with a tree of legal positions . -
Descriptive Set Theory
Descriptive Set Theory David Marker Fall 2002 Contents I Classical Descriptive Set Theory 2 1 Polish Spaces 2 2 Borel Sets 14 3 E®ective Descriptive Set Theory: The Arithmetic Hierarchy 27 4 Analytic Sets 34 5 Coanalytic Sets 43 6 Determinacy 54 7 Hyperarithmetic Sets 62 II Borel Equivalence Relations 73 1 8 ¦1-Equivalence Relations 73 9 Tame Borel Equivalence Relations 82 10 Countable Borel Equivalence Relations 87 11 Hyper¯nite Equivalence Relations 92 1 These are informal notes for a course in Descriptive Set Theory given at the University of Illinois at Chicago in Fall 2002. While I hope to give a fairly broad survey of the subject we will be concentrating on problems about group actions, particularly those motivated by Vaught's conjecture. Kechris' Classical Descriptive Set Theory is the main reference for these notes. Notation: If A is a set, A<! is the set of all ¯nite sequences from A. Suppose <! σ = (a0; : : : ; am) 2 A and b 2 A. Then σ b is the sequence (a0; : : : ; am; b). We let ; denote the empty sequence. If σ 2 A<!, then jσj is the length of σ. If f : N ! A, then fjn is the sequence (f(0); : : :b; f(n ¡ 1)). If X is any set, P(X), the power set of X is the set of all subsets X. If X is a metric space, x 2 X and ² > 0, then B²(x) = fy 2 X : d(x; y) < ²g is the open ball of radius ² around x. Part I Classical Descriptive Set Theory 1 Polish Spaces De¯nition 1.1 Let X be a topological space. -
Descriptive Set Theory and Ω-Powers of Finitary Languages Olivier Finkel, Dominique Lecomte
Descriptive Set Theory and !-Powers of Finitary Languages Olivier Finkel, Dominique Lecomte To cite this version: Olivier Finkel, Dominique Lecomte. Descriptive Set Theory and !-Powers of Finitary Languages. Adrian Rezus. Contemporary Logic and Computing, 1, College Publications, pp.518-541, 2020, Land- scapes in Logic. hal-02898919 HAL Id: hal-02898919 https://hal.archives-ouvertes.fr/hal-02898919 Submitted on 14 Jul 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Descriptive Set Theory and ω-Powers of Finitary Languages Olivier FINKEL and Dominique LECOMTE1 March 18, 2020 • CNRS, Universit´ede Paris, Sorbonne Universit´e, Institut de Math´ematiques de Jussieu-Paris Rive Gauche, Equipe de Logique Math´ematique Campus des Grands Moulins, bˆatiment Sophie-Germain, case 7012, 75205 Paris cedex 13, France fi[email protected] •1 Sorbonne Universit´e, Universit´ede Paris, CNRS, Institut de Math´ematiques de Jussieu-Paris Rive Gauche, Equipe d’Analyse Fonctionnelle Campus Pierre et Marie Curie, case 247, 4, place Jussieu, 75 252 Paris cedex 5, France [email protected] •1 Universit´ede Picardie, I.U.T. de l’Oise, site de Creil, 13, all´ee de la fa¨ıencerie, 60 107 Creil, France Abstract. -
Determinacy and Large Cardinals
Determinacy and Large Cardinals Itay Neeman∗ Abstract. The principle of determinacy has been crucial to the study of definable sets of real numbers. This paper surveys some of the uses of determinacy, concentrating specifically on the connection between determinacy and large cardinals, and takes this connection further, to the level of games of length ω1. Mathematics Subject Classification (2000). 03E55; 03E60; 03E45; 03E15. Keywords. Determinacy, iteration trees, large cardinals, long games, Woodin cardinals. 1. Determinacy Let ωω denote the set of infinite sequences of natural numbers. For A ⊂ ωω let Gω(A) denote the length ω game with payoff A. The format of Gω(A) is displayed in Diagram 1. Two players, denoted I and II, alternate playing natural numbers forming together a sequence x = hx(n) | n < ωi in ωω called a run of the game. The run is won by player I if x ∈ A, and otherwise the run is won by player II. I x(0) x(2) ...... II x(1) x(3) ...... Diagram 1. The game Gω(A). A game is determined if one of the players has a winning strategy. The set A is ω determined if Gω(A) is determined. For Γ ⊂ P(ω ), det(Γ) denotes the statement that all sets in Γ are determined. Using the axiom of choice, or more specifically using a wellordering of the reals, it is easy to construct a non-determined set A. det(P(ωω)) is therefore false. On the other hand it has become clear through research over the years that det(Γ) is true if all the sets in Γ are definable by some concrete means. -
Towards a Descriptive Theory of Cb 0-Spaces
Towards a Descriptive Theory of cb0-Spaces Victor Selivanov A.P. Ershov Institute of Informatics Systems SB RAS Novosibirsk, Russia October 28, 2018 Abstract The paper tries to extend results of the classical Descriptive Set Theory to as many countably based T0-spaces (cb0-spaces) as possible. Along with extending some central facts about Borel, Luzin and Hausdorff hierarchies of sets we consider also the more general case of k-partitions. In particular, we investigate the difference hierarchy of k-partitions and the fine hierarchy closely related to the Wadge hierarchy. Key words. Borel hierarchy, Luzin hierarchy, Hausdorff hierarchy, Wadge reducibility, cb0-space, k-partition, h-preorder, well preorder. 1 Introduction Classical Descriptive Set Theory [Ke95] is an important field of mathematics with numerous applications. It investigates descriptive complexity of sets, functions and equivalence relations in Polish (i.e., separable complete metrizable) spaces. Although Polish spaces are sufficient for many fields of classical mathematics, they are certainly not sufficient for many fields of Theoretical Computer Science where non-Hausdorff spaces (in particular, ω-continuous domains) and non-countably-based spaces (in particular, Kleene-Kreisel continuous func- tionals) are of central importance. For this reason, the task of extending classical Descriptive Set Theory (DST) to as many non-Polish spaces as possible attracted attention of several researchers. Some parts of DST for ω-continuous domains (which are typically non-Polish) were developed in [Se04, Se05a, Se06, Se08]. In [Br13] a good deal of DST was developed for the so called quasi-Polish spaces (see the next section for a definition of this class of cb0-spaces) which include both the Polish spaces and the ω-continuous domains. -
Paul B. Larson a BRIEF HISTORY of DETERMINACY §1. Introduction
Paul B. Larson A BRIEF HISTORY OF DETERMINACY x1. Introduction. Determinacy axioms are statements to the effect that certain games are determined, in that each player in the game has an optimal strategy. The commonly accepted axioms for mathematics, the Zermelo-Fraenkel axioms with the Axiom of Choice (ZFC; see [??, ??]), im- ply the determinacy of many games that people actually play. This applies in particular to many games of perfect information, games in which the players alternate moves which are known to both players, and the out- come of the game depends only on this list of moves, and not on chance or other external factors. Games of perfect information which must end in finitely many moves are determined. This follows from the work of Ernst Zermelo [??], D´enesK}onig[??] and L´aszl´oK´almar[??], and also from the independent work of John von Neumann and Oskar Morgenstern (in their 1944 book, reprinted as [??]). As pointed out by Stanis law Ulam [??], determinacy for games of perfect information of a fixed finite length is essentially a theorem of logic. If we let x1,y1,x2,y2,::: ,xn,yn be variables standing for the moves made by players player I (who plays x1,::: ,xn) and player II (who plays y1,::: ,yn), and A (consisting of sequences of length 2n) is the set of runs of the game for which player I wins, the statement (1) 9x18y1 ::: 9xn8ynhx1; y1; : : : ; xn; yni 2 A essentially asserts that the first player has a winning strategy in the game, and its negation, (2) 8x19y1 ::: 8xn9ynhx1; y1; : : : ; xn; yni 62 A essentially asserts that the second player has a winning strategy.1 We let ! denote the set of natural numbers 0; 1; 2;::: ; for brevity we will often refer to the members of this set as \integers". -
Effective Descriptive Set Theory
E®ective descriptive set theory Yiannis N. Moschovakis UCLA and University of Athens Mostowski100, October 13, 2013 Outline (I) A bit of history (3 slides) (II) The basic notions (7 slides) (III) Some characteristic e®ective results (6 slides) (IV) HYP isomorphism and reducibility (Gregoriades) (3 slides) I Descriptive set theory, ynm, 1980, Second Edition 2009 I Classical descriptive set theory as a re¯nement of e®ective descriptive set theory, ynm, 2010 I Kleene's amazing second recursion theorem, ynm, 2010 I Notes on e®ective descriptive set theory, ynm and Vassilios Gregoriades, in preparation (The ¯rst three are posted on www.math.ucla.edu/»ynm) Yiannis N. Moschovakis: E®ective descriptive set theory 1/20 The arithmetical hierarchy ² Kleene [1943]: The arithmetical hierarchy on subsets of N 0 0 recursive ( §1 (rec. enumerable) ( §2 ( ¢ ¢ ¢ (:§ = ¦; §\¦ = ¢) I Tool for giving easy (semantic) proofs of GÄodel'sFirst Incompleteness Theorem, Tarski's Theorem on the arithmetical unde¯nability of arithmetical truth, etc. ² Mostowski [1947]: Reinvents the arithmetical hierarchy, using as a model the classical projective hierarchy on sets of real numbers 1 1 Borel ( §1 (analytic) ( §2 ( ¢ ¢ ¢ (:§ = ¦; § \ ¦ = ¢) I He grounds the analogy on the two basic results 0 1 Kleene: ¢1 = recursive; Suslin: ¢1 = Borel I Mostowski is unaware of Kleene [1943]: the only post 1939 paper he cites is Post [1944] (He refers to Kleene [1943] in a Postscript added \in press" saying that it \just became available in Poland") Yiannis N. Moschovakis: E®ective descriptive set theory I. A bit of history 1/3 2/20 Mostowski's de¯nition of HYP on N ² Mostowski [1951] introduces the hyperarithmetical hierarchy I In modern notation, roughly, he de¯nes for each constructive CK ordinal » < !1 a universal set for a class P» of subsets of N I The analogy now is between HYP and the Borel sets of reals. -
Structural Dichotomy Theorems in Descriptive Set Theory
Structural dichotomy theorems in descriptive set theory Benjamin Miller Universit¨atWien Winter Semester, 2019 Introduction The goal of these notes is to provide a succinct introduction to the primary structural dichotomy theorems of descriptive set theory. The only prerequisites are a rudimentary knowledge of point-set topology and set theory. Working in the base theory ZF + DC, we first discuss trees, the corresponding representations of closed, Borel, and Souslin sets, and Baire category. We then consider consequences of the open dihypergraph dichotomy and variants of the G0 dichotomy. While pri- marily focused upon Borel structures, we also note that minimal modi- fications of our arguments can be combined with well-known structural consequences of determinacy (which we take as a black box) to yield generalizations into the projective hierarchy and beyond. iii Contents Introduction iii Chapter 1. Preliminaries 1 1. Closed sets 1 2. Ranks 2 3. Borel sets 3 4. Souslin sets 4 5. Baire category 9 6. Canonical objects 13 Chapter 2. The box-open dihypergraph dichotomy 27 1. Colorings of box-open dihypergraphs 27 2. Partial compactifications 31 3. Separation by unions of closed hyperrectangles 34 Chapter 3. The G0 dichotomy, I: Abstract colorings 39 1. Colorings within cliques 39 2. Discrete perfect sets within cliques 42 3. Scrambled sets 45 Chapter 4. The G0 dichotomy, II: Borel colorings 49 1. Borel colorings 49 2. Index two subequivalence relations 52 3. Perfect antichains 54 4. Parametrization and uniformization 56 Chapter 5. The (G0; H0) dichotomy 61 1. Borel local colorings 61 2. Linearizability of quasi-orders 67 Bibliography 71 Index 73 v CHAPTER 1 Preliminaries 1. -
Absoluteness Theorems for Arbitrary Polish Spaces
Revista Colombiana de Matem´aticas Volumen 53(2019)2, p´aginas109-123 Absoluteness theorems for arbitrary Polish spaces Teoremas de absolutidad para espacios polacos arbitrarios Diego Alejandro Mej´ıa1;a;B , Ismael E. Rivera-Madrid2;a 1Shizuoka University, Shizuoka, Japan 2Instituci´onUniversitaria Pascual Bravo, Medell´ın,Colombia Abstract. By coding Polish metric spaces with metrics on countable sets, we propose an interpretation of Polish metric spaces in models of ZFC and extend Mostowski's classical theorem of absoluteness of analytic sets for any Polish metric space in general. In addition, we prove a general version of Shoenfield’s absoluteness theorem. Key words and phrases. Mostowski's Absoluteness Theorem, Shoenfield’s Abso- luteness Theorem, Polish metric spaces. 2010 Mathematics Subject Classification. 03E15, 54H05. Resumen. Mediante la codificaci´onde espacios polacos con m´etricasde con- juntos contables, proponemos una interpretaci´onde espacios m´etricospolacos en modelos de ZFC y extendemos el cl´asicoTeorema de Absolutidad (para conjuntos anal´ıticos)de Mostowski para cualquier espacio m´etrico polaco en general. Adicionalmente, probamos una versi´ongeneral del Teorema de Ab- solutidad de Shoenfield. Palabras y frases clave. Teorema de Absolutidad de Mostowski, Teorema de Absolutidad de Shoenfield, espacios m´etricos polacos. 1. Introduction 1 Mostowski's Absoluteness Theorem (also known as Σ1 absoluteness) states that any analytic subset of the Baire space !! is absolute for transitive mod- els of ZFC. To be more precise, for any tree T ⊆ (! × !)<! the statement 9y 2 !!((x; y) 2 [T ]) is absolute (recall that any closed subset of (! × !)! is 109 110 DIEGO ALEJANDRO MEJ´ıA& ISMAEL E. RIVERA-MADRID characterized by such a tree, so they code all the analytic subsets). -
The Limit View of Infinite Computations
BRICS BRICS RS-94-14 N. Klarlund: The Limit View of Infinite Computations Basic Research in Computer Science The Limit View of Infinite Computations Nils Klarlund BRICS Report Series RS-94-14 ISSN 0909-0878 May 1994 Copyright c 1994, BRICS, Department of Computer Science University of Aarhus. All rights reserved. Reproduction of all or part of this work is permitted for educational or research use on condition that this copyright notice is included in any copy. See back inner page for a list of recent publications in the BRICS Report Series. Copies may be obtained by contacting: BRICS Department of Computer Science University of Aarhus Ny Munkegade, building 540 DK - 8000 Aarhus C Denmark Telephone:+45 8942 3360 Telefax: +45 8942 3255 Internet: [email protected] The Limit View of Innite Computations Nils Klarlund y BRICS Department of Computer Science University of Aarhus Ny Munkegade DK Arhus Denmark klarlunddaimiaaudk Abstract We showhow to view computations involving very general liveness prop erties as limits of nite approximation s This computational mo del do es not require intro duction of innite nondeterminism as with most traditional approaches Our results allow us directly to relate nite computations in order to infer prop erties ab out innite computations Thus we are able to provide a mathematical understanding of what sim ulations and bisimulation s are when liveness is involved In addition we establish links b etween verication theory and classical results in descriptive set theory Our result on simulations is the essential