DOCSLIB.ORG

Constructive Completeness Proofs and Delimited Control Phd Thesis Defence

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Constructive Completeness Proofs and Delimited Control Phd Thesis Defence Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Constructive completeness proofs and delimited control PhD thesis defence Danko Ilik École Polytechnique – INRIA – Université Paris Diderot thesis directed by Hugo Herbelin Paris, October 22, 2010 Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Constructive Mathematics and Computer Science Ï The Curry-Howard correspondence: Ï proofs are programs; Ï theorems are specifications. Ï Constructive type theory and the Coq proof assistant Ï Coq is a tool for developing formal proofs: Ï of theorems in Constructive Mathematics; Ï of correctness of programs with respect to a specification. Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Completeness theorems as programs Ï A formalised Completeness theorem – a tool to switch between model theoretic and proof theory arguments inside Coq Ï Conections between Completeness and Normalisation-by-Evaluation Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Outline Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Outline Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Completeness for standard semantics Theorem (Gödel 1930) A is valid if and only if A is derivable A - derivable there is a derivation tree for A in classical 1st-order logic A - valid Tarski’s truth definition: M A B : M A and M B Í ^ Æ Í Í M A B : M A or M B Í _ Æ Í Í M A B : M A implies M B Í ! Æ Í Í M xA(x): exists t with M A(t) Í 9 Æ Í M xA(x): for any t,M A(t) Í 8 Æ Í M : false Í? Æ Theorem (Krivine 1996) Yes? – Gödel’s proof is constructive, if we allow one more model – the model that validates ? Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Is it constructive? Theorem (McCarty 1996) No? – Completeness implies Markov’s Principle (MP) Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Is it constructive? Theorem (McCarty 1996) No? – Completeness implies Markov’s Principle (MP) Theorem (Krivine 1996) Yes? – Gödel’s proof is constructive, if we allow one more model – the model that validates ? Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic What is the algorithm behind Krivine’s proof? Ï Krivine’s proof carried out in classical 2nd-order arithmetic Ï From the form of the statement, he concludes there is a proof in intuitionistic 2nd-order arithmetic Ï Formalisation in Phox (PA2) by Raffalli; algorithm extracted but “unreadable” Ï Proof unwound in (Berardi-Valentini 2004): main ingredient a constructive ultra-filter theorem Theorem (Berardi-Valentini 2004) Every filter F can be extended to a complete filter Z(F), so that F Z(F) ( F Z(F)) » ? 2 Ã!? 2 Proof. F : F 0 Æ Fn 1 : (Fn {b pbq n,Fn (Fn {b})}) Å Æ"[ [ j Æ »" [ Z : Fn Æ n N 2 Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Constructive Ultra-filter Theorem B countable Boolean algebra Filter subset of B which is inhabited, -closed and · -closed ^ b X a ,...,a X. a a b 2" Æ 9 1 n 2 1 ^ ¢¢¢ ^ n · X-complete (˙ c X ˙ X) c X, for all c B : 2 ¡! ? 2 ¡! 2 2 Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Constructive Ultra-filter Theorem B countable Boolean algebra Filter subset of B which is inhabited, -closed and · -closed ^ b X a ,...,a X. a a b 2" Æ 9 1 n 2 1 ^ ¢¢¢ ^ n · X-complete (˙ c X ˙ X) c X, for all c B : 2 ¡! ? 2 ¡! 2 2 Theorem (Berardi-Valentini 2004) Every filter F can be extended to a complete filter Z(F), so that F Z(F) ( F Z(F)) » ? 2 Ã!? 2 Proof. F : F 0 Æ Fn 1 : (Fn {b pbq n,Fn (Fn {b})}) Å Æ"[ [ j Æ »" [ Z : Fn Æ n N 2 Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic From Ultra-filter theorem to Completeness Instantiate B with the Lindenbaum Boolean algebra: a b : a b · Æ ` a b : (a b) ^ Æ ` : ): If X is a set of axioms, then a Z( X) 2 " means n. ¡ F ( X). ¡ a, 9 9 ⊆ n " ` which implies, ¡ X. ¡ a. 9 ⊆ ` Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Computational content Reflection: (a b) Z a Z b Z ) 2 ¡! 2 ¡! 2 m n max(m,n) 7! 7! Reification: (a Z b Z) (a b) Z 2 ¡! 2 ¡! ) 2 let c : (a b) in Z-complete Æ ) Z-complete is a kind of meta-level : ::E ((c Z Z) Z) c Z 2 ¡!? 2 ¡!? 2 ¡! 2 Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Conclusion Contribution: Ï detailed Henkin-style argument formalised in Type Theory; Ï generalisation to setoids of the Ultra-filter Theorem. Future work: Ï develop a proof/algorithm not parametrised by an enumeration (using delimited control); Ï finish the Coq formalisation. Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Outline Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Classical Completeness via Kripke-style Models Motivation Get a completeness theorem for computational classical calculi – reduction relation should be preserved. Follow Normalization-by-Evaluation (NBE) methodology (Berger-Schwichtenberg 1991): Theorem (Soundness/Evaluation) ¡ A w,w ¡ w A ` ¡!8 ¡! Theorem (Completeness/Reification) ( w,w ¡ w A) ¡ nf A 8 ¡! ¡! ` Corollary (NBE) The composition (Completeness Soundness) normalizes proof ± terms into ´-long ¯-normal form. Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Standard Kripke models Start with a structure (K , ,D, , ), and extend to non-atomic · ? formulas: w A Bw A and w B ^ A Bw A or w B _ A B for any w0 w, if w0 A then w0 B ! ¸ xP(x) for any w0 w and any a D(w0), w0 P(a) 8 ¸ 2 xP(x) there is a D(w) such that w P(a) 9 2 Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Kripke-style models (Call-by-value variant) Like with Kripke models, start with a structure (K , ,D, s, ), and · ? extend strong forcing ( s) to non-atomic formulas: w s A Bw A and w B ^ A Bw A or w B _ A B for any w0 w, if w0 A then w0 B ! ¸ xP(x) for any w0 w and any a D(w0), w0 P(a) 8 ¸ 2 xP(x) there is a D(w) such that w P(a) 9 2 where the non-s-annotated is (non-strong) forcing: w A : w1 w.( w2 w1.w2 sA w2 ) w1 Æ 8 ¸ |8 ¸ {z ! ?} ! ? "refutation"w1:A Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Completeness for Kripke-style models and LK¹¹˜ Theorem (Soundness) c :(¡ ¢) for any w,w ¡ and w : ¢ implies w ` Æ) ? ¡ t : A ¢ for any w,w ¡ and w : ¢ implies w A ` j Æ) ¡ e : A ¢ for any w,w ¡ and w : ¢ implies w : A j ` Æ) Theorem (Completeness) (¡,¢) A there is a term t such that ¡ t : A ¢ Æ) `cf j (¡,¢): A there is an ev. context e such that ¡ e : A ¢ Æ) j `cf Proof. Make a Universal model U from the derivation system: Ï worlds are pairs (¡,¢) Ï strong forcing is cut-free derivability of atoms: (¡,¢) X : t. ¡ t : X ¢ s Æ 9 `cf j exploding nodes are cuts: (¡,¢) : c. c :(¡ cf ¢) Ï ? Æ 9 ` Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Conclusion Ï New notion of model for classical logic Ï Not as simple as Boolean models Ï But, reduction is preserved Ï Dual notion of model that gives call-by-name normalization strategy Ï Proofs formalised in Coq Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Outline Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Completeness of Intuitionistic Logic for Kripke models Ï Kripke models are a standard semantics for intuitionistic logic Ï But, there is no (simple) constructive proof with , : _ 9 Ï classical Henkin-style proofs (Kripke 1965) Ï using Fan Theorem (Veldman 1976) Ï a constructive proof would imply MP (Kreisel 1962) Ï On the other hand, a well-typed functional program for NBE of ¸!_ (Danvy 1996) Ï using delimited-control operators shift and reset (Danvy-Filinski 1989) Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Completeness/NBE for ¸!_ What the problem is Theorem (NBE) A ("reify") : ¡ A ¡ nf A #¡ ¡! ` A ("reflect") : ¡ ne A ¡ A "¡ ` ¡! A B Proof of case _ . " Given a derivation ¡ ne A B, decide: ¡ A or ¡ B? ` _ 1 #(2 S k.k(k4)) Å Å 1 #((¸a.#(2 a))((¸a.#(2 a))4)) ! Å Å Å Å1 #(#(#8)) ! Å Å9 ! Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Shift (S ) and reset (#) delimited control operators Examples #V V ! #F[S k.p] #p{k : ¸x.#F[x]} ! Æ Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Shift (S ) and reset (#) delimited control operators Examples #V V ! #F[S k.p] #p{k : ¸x.#F[x]} ! Æ 1 #(2 S k.k(k4)) Å Å 1 #((¸a.#(2 a))((¸a.#(2 a))4)) ! Å Å Å Å1 #(#(#8)) ! Å Å9 ! Introduction Boolean completeness Classical NBE Intuitionistic NBE Delimited control in Logic Completeness/NBE for ¸!_ Solution of Danvy: use delimited control operators shift (S ) and reset (#) Theorem (NBE) A ("reify") : ¡ A ¡ nf A #¡ ¡! ` A ("reflect") : ¡ ne A ¡ A "¡ ` ¡! A B Proof of case _ .
Load more

Recommended publications
  • Arxiv:1804.02439V1
    DATHEMATICS: A META-ISOMORPHIC VERSION OF ‘STANDARD’ MATHEMATICS BASED ON PROPER CLASSES DANNY ARLEN DE JESUS´ GOMEZ-RAM´ ´IREZ ABSTRACT. We show that the (typical) quantitative considerations about proper (as too big) and small classes are just tangential facts regarding the consistency of Zermelo-Fraenkel Set Theory with Choice. Effectively, we will construct a first-order logic theory D-ZFC (Dual theory of ZFC) strictly based on (a particular sub-collection of) proper classes with a corresponding spe- cial membership relation, such that ZFC and D-ZFC are meta-isomorphic frameworks (together with a more general dualization theorem). More specifically, for any standard formal definition, axiom and theorem that can be described and deduced in ZFC, there exists a corresponding ‘dual’ ver- sion in D-ZFC and vice versa. Finally, we prove the meta-fact that (classic) mathematics (i.e. theories grounded on ZFC) and dathematics (i.e. dual theories grounded on D-ZFC) are meta-isomorphic. This shows that proper classes are as suitable (primitive notions) as sets for building a foundational framework for mathematics. Mathematical Subject Classification (2010): 03B10, 03E99 Keywords: proper classes, NBG Set Theory, equiconsistency, meta-isomorphism. INTRODUCTION At the beginning of the twentieth century there was a particular interest among mathematicians and logicians in finding a general, coherent and con- sistent formal framework for mathematics. One of the main reasons for this was the discovery of paradoxes in Cantor’s Naive Set Theory and related sys- tems, e.g., Russell’s, Cantor’s, Burati-Forti’s, Richard’s, Berry’s and Grelling’s paradoxes [12], [4], [14], [3], [6] and [11].
    [Show full text]
  • Coll041-Endmatter.Pdf
    http://dx.doi.org/10.1090/coll/041 AMERICAN MATHEMATICAL SOCIETY COLLOQUIUM PUBLICATIONS VOLUME 41 A FORMALIZATION OF SET THEORY WITHOUT VARIABLES BY ALFRED TARSKI and STEVEN GIVANT AMERICAN MATHEMATICAL SOCIETY PROVIDENCE, RHODE ISLAND 1985 Mathematics Subject Classification. Primar y 03B; Secondary 03B30 , 03C05, 03E30, 03G15. Library o f Congres s Cataloging-in-Publicatio n Dat a Tarski, Alfred . A formalization o f se t theor y withou t variables . (Colloquium publications , ISS N 0065-9258; v. 41) Bibliography: p. Includes indexes. 1. Se t theory. 2 . Logic , Symboli c an d mathematical . I . Givant, Steve n R . II. Title. III. Series: Colloquium publications (American Mathematical Society) ; v. 41. QA248.T37 198 7 511.3'2 2 86-2216 8 ISBN 0-8218-1041-3 (alk . paper ) Copyright © 198 7 b y th e America n Mathematica l Societ y Reprinted wit h correction s 198 8 All rights reserve d excep t thos e grante d t o th e Unite d State s Governmen t This boo k ma y no t b e reproduce d i n an y for m withou t th e permissio n o f th e publishe r The pape r use d i n thi s boo k i s acid-fre e an d fall s withi n th e guideline s established t o ensur e permanenc e an d durability . @ Contents Section interdependenc e diagram s vii Preface x i Chapter 1 . Th e Formalis m £ o f Predicate Logi c 1 1.1. Preliminarie s 1 1.2.
    [Show full text]
  • Forcing in Proof Theory∗
    Forcing in proof theory¤ Jeremy Avigad November 3, 2004 Abstract Paul Cohen's method of forcing, together with Saul Kripke's related semantics for modal and intuitionistic logic, has had profound e®ects on a number of branches of mathematical logic, from set theory and model theory to constructive and categorical logic. Here, I argue that forcing also has a place in traditional Hilbert-style proof theory, where the goal is to formalize portions of ordinary mathematics in restricted axiomatic theories, and study those theories in constructive or syntactic terms. I will discuss the aspects of forcing that are useful in this respect, and some sample applications. The latter include ways of obtaining conservation re- sults for classical and intuitionistic theories, interpreting classical theories in constructive ones, and constructivizing model-theoretic arguments. 1 Introduction In 1963, Paul Cohen introduced the method of forcing to prove the indepen- dence of both the axiom of choice and the continuum hypothesis from Zermelo- Fraenkel set theory. It was not long before Saul Kripke noted a connection be- tween forcing and his semantics for modal and intuitionistic logic, which had, in turn, appeared in a series of papers between 1959 and 1965. By 1965, Scott and Solovay had rephrased Cohen's forcing construction in terms of Boolean-valued models, foreshadowing deeper algebraic connections between forcing, Kripke se- mantics, and Grothendieck's notion of a topos of sheaves. In particular, Lawvere and Tierney were soon able to recast Cohen's original independence proofs as sheaf constructions.1 It is safe to say that these developments have had a profound impact on most branches of mathematical logic.
    [Show full text]
  • The Strength of Mac Lane Set Theory
    The Strength of Mac Lane Set Theory A. R. D. MATHIAS D´epartement de Math´ematiques et Informatique Universit´e de la R´eunion To Saunders Mac Lane on his ninetieth birthday Abstract AUNDERS MAC LANE has drawn attention many times, particularly in his book Mathematics: Form and S Function, to the system ZBQC of set theory of which the axioms are Extensionality, Null Set, Pairing, Union, Infinity, Power Set, Restricted Separation, Foundation, and Choice, to which system, afforced by the principle, TCo, of Transitive Containment, we shall refer as MAC. His system is naturally related to systems derived from topos-theoretic notions concerning the category of sets, and is, as Mac Lane emphasizes, one that is adequate for much of mathematics. In this paper we show that the consistency strength of Mac Lane's system is not increased by adding the axioms of Kripke{Platek set theory and even the Axiom of Constructibility to Mac Lane's axioms; our method requires a close study of Axiom H, which was proposed by Mitchell; we digress to apply these methods to subsystems of Zermelo set theory Z, and obtain an apparently new proof that Z is not finitely axiomatisable; we study Friedman's strengthening KPP + AC of KP + MAC, and the Forster{Kaye subsystem KF of MAC, and use forcing over ill-founded models and forcing to establish independence results concerning MAC and KPP ; we show, again using ill-founded models, that KPP + V = L proves the consistency of KPP ; turning to systems that are type-theoretic in spirit or in fact, we show by arguments of Coret
    [Show full text]
  • 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 .
    [Show full text]
  • EQUICONSISTENCIES at SUBCOMPACT CARDINALS We
    EQUICONSISTENCIES AT SUBCOMPACT CARDINALS ITAY NEEMAN AND JOHN STEEL Abstract. We present equiconsistency results at the level of subcompact cardinals. Assuming SBHδ , a special case of the Strategic Branches Hypothesis, we prove that if δ is a Woodin cardinal and both 2(δ) and 2δ fail, then δ is subcompact in a class inner 2 + 2 model. If in addition (δ ) fails, we prove that δ is Π1 subcompact in a class inner model. These results are optimal, and lead to equiconsistencies. As a corollary we also see that assuming the existence of a Woodin cardinal δ so that SBHδ holds, the Proper Forcing 2 Axiom implies the existence of a class inner model with a Π1 subcompact cardinal. Our methods generalize to higher levels of the large cardinal hierarchy, that involve long extenders, and large cardinal axioms up to δ is δ+(n) supercompact for all n < !. We state some results at this level, and indicate how they are proved. MSC 2010: 03E45, 03E55. Keywords: subcompact cardinals, inner models, long extenders, coherent sequences, square. We dedicate this paper to Rich Laver, a brilliant mathematician and a kind and generous colleague. x1. Introduction. We present equiconsistency results at the level of sub- compact cardinals. The methods we use extend further, to levels which are interlaced with the axioms κ is κ+(n) supercompact, for n < !. The extensions will be carried out in a sequel to this paper, Neeman-Steel [7], but we indicate in this paper some of the main ideas involved. Our reversals assume iterability for countable substructures of V .
    [Show full text]
  • Generalized Solovay Measures, the HOD Analysis, and the Core Model Induction
    Generalized Solovay Measures, the HOD Analysis, and the Core Model Induction by Nam Duc Trang A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Mathematics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor John Steel, Chair Professor W. Hugh Woodin Professor Sherrilyn Roush Fall 2013 Generalized Solovay Measures, the HOD Analysis, and the Core Model Induction Copyright 2013 by Nam Duc Trang 1 Abstract Generalized Solovay Measures, the HOD Analysis, and the Core Model Induction by Nam Duc Trang Doctor of Philosophy in Mathematics University of California, Berkeley Professor John Steel, Chair This thesis belongs to the field of descriptive inner model theory. Chapter 1 provides a proper context for this thesis and gives a brief introduction to the theory of AD+, the theory of hod mice, and a definition of KJ (R). In Chapter 2, we explore the theory of generalized Solovay measures. We prove structure theorems concerning canonical models of the theory \AD+ + there is a generalized Solovay measure" and compute the exact consistency strength of this theory. We also give some applications relating generalized Solovay measures to the determinacy of a class of long games. In Chapter 3, we give a HOD analysis of AD+ + V = L(P(R)) models below \ADR + Θ is regular." This is an application of the theory of hod mice developed in [23]. We also analyze HOD of AD+-models of the form V = L(R; µ) where µ is a generalized Solovay measure. In Chapter 4, we develop techniques for the core model induction.
    [Show full text]
  • Metamathematics in Coq Metamathematica in Coq (Met Een Samenvatting in Het Nederlands)
    Metamathematics in Coq Metamathematica in Coq (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de Rector Magnificus, Prof. dr. W.H. Gispen, ingevolge het besluit van het College voor Promoties in het openbaar te verdedigen op vrijdag 31 oktober 2003 des middags te 14:30 uur door Roger Dimitri Alexander Hendriks geboren op 6 augustus 1973 te IJsselstein. Promotoren: Prof. dr. J.A. Bergstra (Faculteit der Wijsbegeerte, Universiteit Utrecht) Prof. dr. M.A. Bezem (Institutt for Informatikk, Universitetet i Bergen) Voor Nelleke en Ole. Preface The ultimate arbiter of correctness is formalisability. It is a widespread view amongst mathematicians that correct proofs can be written out completely for- mally. This means that, after ‘unfolding’ the layers of abbreviations and con- ventions on which the presentation of a mathematical proof usually depends, the validity of every inference step should be completely perspicuous by a pre- sentation of this step in an appropriate formal language. When descending from the informal heat to the formal cold,1 we can rely less on intuition and more on formal rules. Once we have convinced ourselves that those rules are sound, we are ready to believe that the derivations they accept are correct. Formalis- ing reduces the reliability of a proof to the reliability of the means of verifying it ([60]). Formalising is more than just filling-in the details, it is a creative and chal- lenging job. It forces one to make decisions that informal presentations often leave unspecified. The search for formal definitions that, on the one hand, con- vincingly represent the concepts involved and, on the other hand, are convenient for formal proof, often elucidates the informal presentation.
    [Show full text]
  • A Variant of Church's Set Theory with a Universal Set in Which The
    A Variant of Church’s Set Theory with a Universal Set in which the Singleton Function is a Set Flash Sheridan 101 Alma Street #704 Palo Alto, California 94301-1008 USA http://pobox.com/~flash 3 January 2013, minor revisions 21 December 2013 Abstract A Platonistic set theory with a universal set, CUSι, in the spirit of Alonzo Church’s “Set Theory with a Universal Set,” is presented; this theory uses a different sequence of restricted equivalence relations from Church’s, such that the singleton function is a 2-equivalence class and hence a set, but (like Emerson Mitchell’s set theory, and unlike Church’s), it lacks unrestricted axioms of sum and product set. The theory has an axiom of unrestricted pairwise union, however, and unrestricted complements. An interpretation of the axioms in a set theory similar to Zermelo-Fraenkel set theory with global choice and urelements (which play the rôle of new sets) is presented, and the interpretations of the axioms proved, which proves their relative consistency. The verifications of the basic axioms are performed in consider- ably greater generality than necessary for the main result, to answer a query of Thomas Forster and Richard Kaye. The existence of the singleton function partially rebuts a conjecture of Church about the unification of his set theory with Quine’s New Foundations, but the natural extension of the theory leads to a variant of the Russell paradox. An abridged version of this article will appear in Logique et Analyse. This unabridged version is to be made available on the web site of the Centre National de Recherches de Logique, http://www.logic-center.be/Publications/Bibliotheque.
    [Show full text]
  • From Constructive Mathematics to Computable Analysis Via the Realizability Interpretation
    From Constructive Mathematics to Computable Analysis via the Realizability Interpretation Vom Fachbereich Mathematik der Technischen Universit¨atDarmstadt zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigte Dissertation von Dipl.-Math. Peter Lietz aus Mainz Referent: Prof. Dr. Thomas Streicher Korreferent: Dr. Alex Simpson Tag der Einreichung: 22. Januar 2004 Tag der m¨undlichen Pr¨ufung: 11. Februar 2004 Darmstadt 2004 D17 Hiermit versichere ich, dass ich diese Dissertation selbst¨andig verfasst und nur die angegebenen Hilfsmittel verwendet habe. Peter Lietz Abstract Constructive mathematics is mathematics without the use of the principle of the excluded middle. There exists a wide array of models of constructive logic. One particular interpretation of constructive mathematics is the realizability interpreta- tion. It is utilized as a metamathematical tool in order to derive admissible rules of deduction for systems of constructive logic or to demonstrate the equiconsistency of extensions of constructive logic. In this thesis, we employ various realizability mod- els in order to logically separate several statements about continuity in constructive mathematics. A trademark of some constructive formalisms is predicativity. Predicative logic does not allow the definition of a set by quantifying over a collection of sets that the set to be defined is a member of. Starting from realizability models over a typed version of partial combinatory algebras we are able to show that the ensuing models provide the features necessary in order to interpret impredicative logics and type theories if and only if the underlying typed partial combinatory algebra is equivalent to an untyped pca. It is an ongoing theme in this thesis to switch between the worlds of classical and constructive mathematics and to try and use constructive logic as a method in order to obtain results of interest also for the classically minded mathematician.
    [Show full text]
  • Topological Interpretations of Provability Logic
    Topological interpretations of provability logic Lev Beklemishev∗ David Gabelaia† May 2, 2018 Abstract Provability logic concerns the study of modality ✷ as provability in formal systems such as Peano arithmetic. Natural, albeit quite surprising, topological interpretation of provability logic has been found in the 1970’s by Harold Simmons and Leo Esakia. They have observed that the dual ✸ modality, corresponding to consistency in the context of formal arithmetic, has all the basic properties of the topological derivative operator acting on a scattered space. The topic has become a long-term project for the Georgian school of logic led by Esakia, with occasional contributions from elsewhere. More recently, a new impetus came from the study of polymodal provability logic GLP that was known to be Kripke incomplete and, in general, to have a more complicated behavior than its unimodal counterpart. Topological semantics provided a better alternative to Kripke models in the sense that GLP was shown to be topologically complete. At the same time, new fascinating connections with set theory and large cardinals have emerged. We give a survey of the results on topological semantics of provability logic starting from first contributions by Esakia. However, a special emphasis is put on the recent work on topological models of polymodal provability logic. We also included a few results that have not been published so far, most notably the results of Section 6 (due the second author) and Sections 10, 11 (due to the first author). 1 Provability algebras and logics Provability logics and algebras emerge from, respectively, a modal logical and an arXiv:1210.7317v1 [math.LO] 27 Oct 2012 algebraic point of view on the proof-theoretic phenomena around G¨odel’s incom- pleteness theorems.
    [Show full text]
  • UC Berkeley UC Berkeley Electronic Theses and Dissertations
    UC Berkeley UC Berkeley Electronic Theses and Dissertations Title Interactions between computability theory and set theory Permalink https://escholarship.org/uc/item/5hn678b1 Author Schweber, Noah Publication Date 2016 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California Interactions between computability theory and set theory by Noah Schweber A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Mathematics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Antonio Montalban, Chair Professor Leo Harrington Professor Wesley Holliday Spring 2016 Interactions between computability theory and set theory Copyright 2016 by Noah Schweber i To Emma ii Contents Contents ii 1 Introduction1 1.1 Higher reverse mathematics ........................... 1 1.2 Computability in generic extensions....................... 3 1.3 Further results .................................. 5 2 Higher reverse mathematics, 1/28 2.1 Introduction.................................... 8 2.2 Reverse mathematics beyond type 1....................... 11 2.3 Separating clopen and open determinacy.................... 25 2.4 Conclusion..................................... 38 3 Higher reverse mathematics, 2/2 41 3 3.1 The strength of RCA0 ............................... 41 3.2 Choice principles ................................. 50 4 Computable structures in generic extensions 54 4.1 Introduction...................................
    [Show full text]