Foundations of Mathematics from the Perspective of Computer Verification
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“The Church-Turing “Thesis” As a Special Corollary of Gödel's
“The Church-Turing “Thesis” as a Special Corollary of Gödel’s Completeness Theorem,” in Computability: Turing, Gödel, Church, and Beyond, B. J. Copeland, C. Posy, and O. Shagrir (eds.), MIT Press (Cambridge), 2013, pp. 77-104. Saul A. Kripke This is the published version of the book chapter indicated above, which can be obtained from the publisher at https://mitpress.mit.edu/books/computability. It is reproduced here by permission of the publisher who holds the copyright. © The MIT Press The Church-Turing “ Thesis ” as a Special Corollary of G ö del ’ s 4 Completeness Theorem 1 Saul A. Kripke Traditionally, many writers, following Kleene (1952) , thought of the Church-Turing thesis as unprovable by its nature but having various strong arguments in its favor, including Turing ’ s analysis of human computation. More recently, the beauty, power, and obvious fundamental importance of this analysis — what Turing (1936) calls “ argument I ” — has led some writers to give an almost exclusive emphasis on this argument as the unique justification for the Church-Turing thesis. In this chapter I advocate an alternative justification, essentially presupposed by Turing himself in what he calls “ argument II. ” The idea is that computation is a special form of math- ematical deduction. Assuming the steps of the deduction can be stated in a first- order language, the Church-Turing thesis follows as a special case of G ö del ’ s completeness theorem (first-order algorithm theorem). I propose this idea as an alternative foundation for the Church-Turing thesis, both for human and machine computation. Clearly the relevant assumptions are justified for computations pres- ently known. -
Weyl's Predicative Classical Mathematics As a Logic-Enriched
Weyl’s Predicative Classical Mathematics as a Logic-Enriched Type Theory? Robin Adams and Zhaohui Luo Dept of Computer Science, Royal Holloway, Univ of London {robin,zhaohui}@cs.rhul.ac.uk Abstract. In Das Kontinuum, Weyl showed how a large body of clas- sical mathematics could be developed on a purely predicative founda- tion. We present a logic-enriched type theory that corresponds to Weyl’s foundational system. A large part of the mathematics in Weyl’s book — including Weyl’s definition of the cardinality of a set and several re- sults from real analysis — has been formalised, using the proof assistant Plastic that implements a logical framework. This case study shows how type theory can be used to represent a non-constructive foundation for mathematics. Key words: logic-enriched type theory, predicativism, formalisation 1 Introduction Type theories have proven themselves remarkably successful in the formalisation of mathematical proofs. There are several features of type theory that are of particular benefit in such formalisations, including the fact that each object carries a type which gives information about that object, and the fact that the type theory itself has an inbuilt notion of computation. These applications of type theory have proven particularly successful for the formalisation of intuitionistic, or constructive, proofs. The correspondence between terms of a type theory and intuitionistic proofs has been well studied. The degree to which type theory can be used for the formalisation of other notions of proof has been investigated to a much lesser degree. There have been several formalisations of classical proofs by adapting a proof checker intended for intuitionistic mathematics, say by adding the principle of excluded middle as an axiom (such as [Gon05]). -
The Cyber Entscheidungsproblem: Or Why Cyber Can’T Be Secured and What Military Forces Should Do About It
THE CYBER ENTSCHEIDUNGSPROBLEM: OR WHY CYBER CAN’T BE SECURED AND WHAT MILITARY FORCES SHOULD DO ABOUT IT Maj F.J.A. Lauzier JCSP 41 PCEMI 41 Exercise Solo Flight Exercice Solo Flight Disclaimer Avertissement Opinions expressed remain those of the author and Les opinons exprimées n’engagent que leurs auteurs do not represent Department of National Defence or et ne reflètent aucunement des politiques du Canadian Forces policy. This paper may not be used Ministère de la Défense nationale ou des Forces without written permission. canadiennes. Ce papier ne peut être reproduit sans autorisation écrite. © Her Majesty the Queen in Right of Canada, as © Sa Majesté la Reine du Chef du Canada, représentée par represented by the Minister of National Defence, 2015. le ministre de la Défense nationale, 2015. CANADIAN FORCES COLLEGE – COLLÈGE DES FORCES CANADIENNES JCSP 41 – PCEMI 41 2014 – 2015 EXERCISE SOLO FLIGHT – EXERCICE SOLO FLIGHT THE CYBER ENTSCHEIDUNGSPROBLEM: OR WHY CYBER CAN’T BE SECURED AND WHAT MILITARY FORCES SHOULD DO ABOUT IT Maj F.J.A. Lauzier “This paper was written by a student “La présente étude a été rédigée par un attending the Canadian Forces College stagiaire du Collège des Forces in fulfilment of one of the requirements canadiennes pour satisfaire à l'une des of the Course of Studies. The paper is a exigences du cours. L'étude est un scholastic document, and thus contains document qui se rapporte au cours et facts and opinions, which the author contient donc des faits et des opinions alone considered appropriate and que seul l'auteur considère appropriés et correct for the subject. -
Model Theory, Arithmetic & Algebraic Geometry
MODEL THEORY, ARITHMETIC & ALGEBRAIC GEOMETRY JOEL TORRES DEL VALLE 1. LANGUAGES AND STRUCTURES. 1.1. What is Model Theory? Model Theory is the study of the relationship between theories and mathematical struc- tures which satisfies them [11]. Model Theory introduces Mathematical Logic in the prac- tice of Universal Algebra, so we can think it like Model Theory = Universal Algebra + Mathematical Logic. I started this pages with the same question Chang-Keisler started their celebrated book [3]: ‘What is Model Theory?’ They also summarize the answer to the equation above. In this pages I summarize the relationship between Model Theory, Arithmetic and Algebraic Geometry. The topics will be the basic ones in the area, so this is just an invitation, in the presentation of topics I mainly follow the philosophy of the references, my basic reference is [9]. The early pioneers in Model Theory were Leopold L¨owenheim in 1915, in his work ‘Uber¨ M¨oglichkeiten im Relativkalk¨ul’1 there he proved that if a first order theory T that has an infinite model then has a countable model. Thoralf Skolem in 1920 proved a second version of L¨owenheim result, in his work ‘Logisch-kombinatorische Untersuchungen ¨uber die Erf¨ullbarkeit oder Beweisbarkeit mathematischer S¨atze nebst einem Theoreme ¨uber dichte Mengen’2. Kurt G¨odel in 1930 proved his Completeness and Compactness Theorems for countable languages in his Doctoral dissertation at the University of Viena titled ‘Die Vollst¨andigkeit der Axiome des logischen Funktionenkalk¨uls’3. Alfred Tarski in 1931 -
Starting the Dismantling of Classical Mathematics
Australasian Journal of Logic Starting the Dismantling of Classical Mathematics Ross T. Brady La Trobe University Melbourne, Australia [email protected] Dedicated to Richard Routley/Sylvan, on the occasion of the 20th anniversary of his untimely death. 1 Introduction Richard Sylvan (n´eRoutley) has been the greatest influence on my career in logic. We met at the University of New England in 1966, when I was a Master's student and he was one of my lecturers in the M.A. course in Formal Logic. He was an inspirational leader, who thought his own thoughts and was not afraid to speak his mind. I hold him in the highest regard. He was very critical of the standard Anglo-American way of doing logic, the so-called classical logic, which can be seen in everything he wrote. One of his many critical comments was: “G¨odel's(First) Theorem would not be provable using a decent logic". This contribution, written to honour him and his works, will examine this point among some others. Hilbert referred to non-constructive set theory based on classical logic as \Cantor's paradise". In this historical setting, the constructive logic and mathematics concerned was that of intuitionism. (The Preface of Mendelson [2010] refers to this.) We wish to start the process of dismantling this classi- cal paradise, and more generally classical mathematics. Our starting point will be the various diagonal-style arguments, where we examine whether the Law of Excluded Middle (LEM) is implicitly used in carrying them out. This will include the proof of G¨odel'sFirst Theorem, and also the proof of the undecidability of Turing's Halting Problem. -
Henkin's Method and the Completeness Theorem
Henkin's Method and the Completeness Theorem Guram Bezhanishvili∗ 1 Introduction Let L be a first-order logic. For a sentence ' of L, we will use the standard notation \` '" for ' is provable in L (that is, ' is derivable from the axioms of L by the use of the inference rules of L); and \j= '" for ' is valid (that is, ' is satisfied in every interpretation of L). The soundness theorem for L states that if ` ', then j= '; and the completeness theorem for L states that if j= ', then ` '. Put together, the soundness and completeness theorems yield the correctness theorem for L: a sentence is derivable in L iff it is valid. Thus, they establish a crucial feature of L; namely, that syntax and semantics of L go hand-in-hand: every theorem of L is a logical law (can not be refuted in any interpretation of L), and every logical law can actually be derived in L. In fact, a stronger version of this result is also true. For each first-order theory T and a sentence ' (in the language of T ), we have that T ` ' iff T j= '. Thus, each first-order theory T (pick your favorite one!) is sound and complete in the sense that everything that we can derive from T is true in all models of T , and everything that is true in all models of T is in fact derivable from T . This is a very strong result indeed. One possible reading of it is that the first-order formalization of a given mathematical theory is adequate in the sense that every true statement about T that can be formalized in the first-order language of T is derivable from the axioms of T . -
A Quasi-Classical Logic for Classical Mathematics
Theses Honors College 11-2014 A Quasi-Classical Logic for Classical Mathematics Henry Nikogosyan University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/honors_theses Part of the Logic and Foundations Commons Repository Citation Nikogosyan, Henry, "A Quasi-Classical Logic for Classical Mathematics" (2014). Theses. 21. https://digitalscholarship.unlv.edu/honors_theses/21 This Honors Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Honors Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/or on the work itself. This Honors Thesis has been accepted for inclusion in Theses by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. A QUASI-CLASSICAL LOGIC FOR CLASSICAL MATHEMATICS By Henry Nikogosyan Honors Thesis submitted in partial fulfillment for the designation of Departmental Honors Department of Philosophy Ian Dove James Woodbridge Marta Meana College of Liberal Arts University of Nevada, Las Vegas November, 2014 ABSTRACT Classical mathematics is a form of mathematics that has a large range of application; however, its application has boundaries. In this paper, I show that Sperber and Wilson’s concept of relevance can demarcate classical mathematics’ range of applicability by demarcating classical logic’s range of applicability. -
Mathematical Languages Shape Our Understanding of Time in Physics Physics Is Formulated in Terms of Timeless, Axiomatic Mathematics
comment Corrected: Publisher Correction Mathematical languages shape our understanding of time in physics Physics is formulated in terms of timeless, axiomatic mathematics. A formulation on the basis of intuitionist mathematics, built on time-evolving processes, would ofer a perspective that is closer to our experience of physical reality. Nicolas Gisin n 1922 Albert Einstein, the physicist, met in Paris Henri Bergson, the philosopher. IThe two giants debated publicly about time and Einstein concluded with his famous statement: “There is no such thing as the time of the philosopher”. Around the same time, and equally dramatically, mathematicians were debating how to describe the continuum (Fig. 1). The famous German mathematician David Hilbert was promoting formalized mathematics, in which every real number with its infinite series of digits is a completed individual object. On the other side the Dutch mathematician, Luitzen Egbertus Jan Brouwer, was defending the view that each point on the line should be represented as a never-ending process that develops in time, a view known as intuitionistic mathematics (Box 1). Although Brouwer was backed-up by a few well-known figures, like Hermann Weyl 1 and Kurt Gödel2, Hilbert and his supporters clearly won that second debate. Hence, time was expulsed from mathematics and mathematical objects Fig. 1 | Debating mathematicians. David Hilbert (left), supporter of axiomatic mathematics. L. E. J. came to be seen as existing in some Brouwer (right), proposer of intuitionist mathematics. Credit: Left: INTERFOTO / Alamy Stock Photo; idealized Platonistic world. right: reprinted with permission from ref. 18, Springer These two debates had a huge impact on physics. -
The Z of ZF and ZFC and ZF¬C
From SIAM News , Volume 41, Number 1, January/February 2008 The Z of ZF and ZFC and ZF ¬C Ernst Zermelo: An Approach to His Life and Work. By Heinz-Dieter Ebbinghaus, Springer, New York, 2007, 356 pages, $64.95. The Z, of course, is Ernst Zermelo (1871–1953). The F, in case you had forgotten, is Abraham Fraenkel (1891–1965), and the C is the notorious Axiom of Choice. The book under review, by a prominent logician at the University of Freiburg, is a splendid in-depth biography of a complex man, a treatment that shies away neither from personal details nor from the mathematical details of Zermelo’s creations. BOOK R EV IEW Zermelo was a Berliner whose early scientific work was in applied By Philip J. Davis mathematics: His PhD thesis (1894) was in the calculus of variations. He had thought about this topic for at least ten additional years when, in 1904, in collaboration with Hans Hahn, he wrote an article on the subject for the famous Enzyclopedia der Mathematische Wissenschaften . In point of fact, though he is remembered today primarily for his axiomatization of set theory, he never really gave up applications. In his Habilitation thesis (1899), Zermelo was arguing with Ludwig Boltzmann about the foun - dations of the kinetic theory of heat. Around 1929, he was working on the problem of the path of an airplane going in minimal time from A to B at constant speed but against a distribution of winds. This was a problem that engaged Levi-Civita, von Mises, Carathéodory, Philipp Frank, and even more recent investigators. -
Lambda Calculus and the Decision Problem
Lambda Calculus and the Decision Problem William Gunther November 8, 2010 Abstract In 1928, Alonzo Church formalized the λ-calculus, which was an attempt at providing a foundation for mathematics. At the heart of this system was the idea of function abstraction and application. In this talk, I will outline the early history and motivation for λ-calculus, especially in recursion theory. I will discuss the basic syntax and the primary rule: β-reduction. Then I will discuss how one would represent certain structures (numbers, pairs, boolean values) in this system. This will lead into some theorems about fixed points which will allow us have some fun and (if there is time) to supply a negative answer to Hilbert's Entscheidungsproblem: is there an effective way to give a yes or no answer to any mathematical statement. 1 History In 1928 Alonzo Church began work on his system. There were two goals of this system: to investigate the notion of 'function' and to create a powerful logical system sufficient for the foundation of mathematics. His main logical system was later (1935) found to be inconsistent by his students Stephen Kleene and J.B.Rosser, but the 'pure' system was proven consistent in 1936 with the Church-Rosser Theorem (which more details about will be discussed later). An application of λ-calculus is in the area of computability theory. There are three main notions of com- putability: Hebrand-G¨odel-Kleenerecursive functions, Turing Machines, and λ-definable functions. Church's Thesis (1935) states that λ-definable functions are exactly the functions that can be “effectively computed," in an intuitive way. -
On Synthetic Undecidability in Coq, with an Application to the Entscheidungsproblem
On Synthetic Undecidability in Coq, with an Application to the Entscheidungsproblem Yannick Forster Dominik Kirst Gert Smolka Saarland University Saarland University Saarland University Saarbrücken, Germany Saarbrücken, Germany Saarbrücken, Germany [email protected] [email protected] [email protected] Abstract like decidability, enumerability, and reductions are avail- We formalise the computational undecidability of validity, able without reference to a concrete model of computation satisfiability, and provability of first-order formulas follow- such as Turing machines, general recursive functions, or ing a synthetic approach based on the computation native the λ-calculus. For instance, representing a given decision to Coq’s constructive type theory. Concretely, we consider problem by a predicate p on a type X, a function f : X ! B Tarski and Kripke semantics as well as classical and intu- with 8x: p x $ f x = tt is a decision procedure, a function itionistic natural deduction systems and provide compact д : N ! X with 8x: p x $ ¹9n: д n = xº is an enumer- many-one reductions from the Post correspondence prob- ation, and a function h : X ! Y with 8x: p x $ q ¹h xº lem (PCP). Moreover, developing a basic framework for syn- for a predicate q on a type Y is a many-one reduction from thetic computability theory in Coq, we formalise standard p to q. Working formally with concrete models instead is results concerning decidability, enumerability, and reducibil- cumbersome, given that every defined procedure needs to ity without reference to a concrete model of computation. be shown representable by a concrete entity of the model. -
Classical Metalogic an Introduction to Classical Model Theory & Computability
Classical Metalogic An Introduction to Classical Model Theory & Computability Notes by R.J. Buehler January 5, 2015 2 Preface What follows are my personal notes created in preparation for the UC-Berkeley Group in Logic preliminary exam. I am not a computability theorist, nor a model theorist; I am a graduate student with some knowledge who is–alas–quite fallible. Accordingly, this text is made available as a convenient reference, set of notes, and summary, but without even the slight hint of a guarantee that everything contained within is factual and correct (indeed, some areas are entirely unchanged from the moment I copied them off the blackboard). This said, if you find a serious error, I would greatly appreciate it if you would let me know so that it can be corrected. The material for these notes derives from a wide variety of sources: Lectures by Wes Holliday Lectures by Antonio Montalban Lectures by John Steel Kevin Kelly’s computability theory notes David Marker’s “Model Theory: An Introduction” Wilfrid Hodge’s “A Shorter Model Theory” Robert Soare’s “Recursively Enumerable Sets and Degrees" Richard Kaye’s “Models of Peano Arithmetic” Chang and Keisler’s “Model Theory" While I certainly hope my notes are beneficial, if you’re attempting to learn the contained material for the first time, I would highly suggest picking up (at least) a copy of Marker and Soare’s texts in addition. To those Group in Logic students who may be using these notes to help themselves prepare for their preliminary exam, chapters 1-5, 7, and 9-18 contain relevant material, as well as chapter 8, section 3.