DOCSLIB.ORG

Diagonalizing by Fixed-Points

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Diagonalizing by Fixed-Points Ahmad Karimi Tel: +98 (0)919 510 2790 Department of Mathematics Fax: +98 (0)21 8288 3493 Tarbiat Modares University E-mail:[email protected] P.O.Box 14115{134 Behbahan KA Univ. of Tech. Tehran, IRAN 61635{151 Behbahan, IRAN Saeed Salehi Tel: +98 (0)411 339 2905 Department of Mathematics Fax: +98 (0)411 334 2102 University of Tabriz E-mail:/[email protected]/ Σα∂ ir Σα`}{ P.O.Box 51666{17766 /[email protected]/ u Tabriz, IRAN Web: http://SaeedSalehi.ir/ Diagonalizing by Fixed{Points Abstract A universal schema for diagonalization was popularized by N. S. Yanofsky (2003) in which the existence of a (diagonolized-out and contradictory) object implies the existence of a fixed-point for a certain function. It was shown that many self-referential paradoxes and diagonally proved theorems can fit in that schema. Here, we fit more theorems in the universal schema of diagonalization, such as Euclid's theorem on the infinitude of the primes and new proofs of G. Boolos (1997) for Cantor's theorem on the non-equinumerosity of a set with its powerset. Then, in Linear Temporal Logic, we show the non-existence of a fixed-point in this logic whose proof resembles the argument of Yablo's paradox. Thus, Yablo's paradox turns for the first time into a genuine mathematico-logical theorem in the framework of Linear Temporal Logic. Again the diagonal schema of the paper is used in this proof; and also it is shown that G. Priest's inclosure schema (1997) can fit in our universal diagonal/fixed-point schema. We also show the existence of dominating (Ackermann-like) functions arXiv:1303.0730v5 [math.LO] 10 Dec 2016 (which dominate a given countable set of functions|like primitive recursives) using the schema. vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv 2010 Mathematics Subject Classification: 18A10 · 18A15 · 03B44 · 03A05. Keywords: Diagonalization · Self-Reference · Fixed-Points · Cantor's Theorem · Euclid's Theorem · Yablo's Paradox · Ackermann's Function · Dominating Functions · (Linear) Temporal Logic. Date: 30.08.14 (30 August 2014) page 1 (of 12) page 2 (of 12) Diagonalizing by Fixed{Points 1 Introduction Cantor's Diagonal Argument was introduced in his (third proof for the) famous theorem on non{ denumerability of the reals; the argument shows that there can be no surjection from a set A to its powerset P(A): for any function F : A ! P(A) the set DF = fx 2 A j x 62 F (x)g is not in the range of F because for any a 2 A we have a 2 DF ! a 62 F (a), and so a 2 (DF n F (a)) [ (F (a) n DF ), whence DF 6= F (a). This argument shows up also in Russell's Paradox: the collection R = fx j x 62 xg of sets is not a set, since for any set A we have A 2 R ! A 62 A, so A 6= R. One other example is Turing's Halting Problem in Computability Theory: if W0;W1;W2; ··· is the family of all re sets (recursively enu- merable subsets of N), then the set K = fn 2 N j n 62 Wng is not re, because for any re set Wm we have m 2 K ! m 62 Wm, and so m 2 (K n Wm) [ (Wm n K), thus K 6= Wm. It can be seen that the (diagonal) set K = fn 2 N j n 2 Wng is an re but undecidable set. Many other theorems in mathematics (logic, set theory, computability theory, complexity theory, etc.) use diagonal arguments; Tarski's theorem on the undefinability of truth, and Godel¨ 's theorem on the incompleteness of sufficiently strong and (!{)consistent theories are two prominent examples. In 2003, Noson S. Yanofsky published the paper [14] mentioning some earlier descriptions for \many of the classical paradoxes and incompleteness theorems in a categorial fashion", in the sense that by using \the language of category theory (and of cartesian closed categories in particular)" one can demonstrate some paradoxical phenomena and show the above mentioned theorems of Cantor, Tarski and Godel¨ ; the goal of [14] was \to make these amazing results available to a larger audience". In that paper, a universal schema has been considered in the language of sets and functions (not categories) and the paradoxes of the Liar, the strong liar, Russell, Grelling, Richard, Time Travel, and Lob¨ , and the theorems of Cantor (A P(A)), Turing (undecidability of the Halting problem, and existence of a non{ re set), Baker-Gill-Solovay (the existence of an oracle O such that PO 6= NPO), Carnap (the diagonalization lemma), Godel¨ (first incompleteness theorem), Rosser (incompleteness of sufficiently strong and consistent theories), Tarski (undefinability of truth in sufficiently strong languages), Parikh (existence of sentences with very long proofs), Kleene (Recursion Theorem), Rice (undecidability of non{ trivial properties of recursive functions), and von Neumann (existence of self{reproducing machines) are shown as instances. In this paper, we fit some other theorems and proofs into the above mentioned universal schema of Yanofsky; these include Euclid's Theorem on the infinitude of the primes, Boolos' proof of the existence of some explicitly definable counterexamples to the non{injectivity of functions F : P(A) ! A for any set A, Yablo's paradox in a form of a mathematical theorem in the framework of linear temporal logic as a non{existence of some certain fixed–points, and the existence of dominating functions for a given countable set of functions like Ackermann's function which dominates all the primitive recursive functions. In the rest of the introduction we fix our notation and introduce the common framework. 1.1 Cantor's Theorem by Fixed{Points Let B, C and D be arbitrary sets. Any function f : B × C ! D corresponds to a function fb : C ! DB where fb(c)(b) = f(b; c) for any b 2 B and c 2 C (the set DB consists of all the functions from B to D). Conversely, for any function F : C ! DB there exists some f : B × C ! D such that fb = F : for any B×C ∼ B C b 2 B and c 2 C let f(b; c) = F (c)(b). In the other words −b : D = (D ) . Let f : B × C ! D be a fixed function. A function g : B ! D is called representable by f at a fixed c0 2 C, when for any x 2 B, B g(x) = f(x; c0) holds. In the other words, g = fb(c0). So, the function fb : C ! D is onto if and only if every function B ! D is representable by f at some c0 2 C. MANUSCRIPT (Submitted) Σα∂ c Ahmad Karimi & Saeed Salehi 2014 ir uΣα`}{ Diagonalizing by Fixed{Points page 3 (of 12) Theorem 1.1 (Cantor) Assume the function α : D −! D, for a set D, does not have any fixed point (i.e., α(d) 6= d for all d 2 D). Then for any set B and any function f : B × B ! D there exists a function g : B ! D that is not representable by f (i.e., for all b 2 B, g(−) 6= f(−; b)). Proof. The desired function g : x 7! α(f(x; x)) can be constructed as follows: f B × B - D 6 4B α ? B - D g where 4B is the diagonal function of B (4B(x) = hx; xi). If g is representable by f at b 2 B, then g(x) = f(x; b) for any x 2 B, and in particular g(b) = f(b; b). On the other hand by the definition of g we have g(x) = α(f(x; x)) and in particular (for x = b) g(b) = α(f(b; b)). It follows that f(b; b) is a fixed–point of α; contradiction. Whence, the function g is not representable by f (at any b 2 B). o For any set A we have P(A) ∼= 2A where 2 = f0; 1g and 2A is the set of all functions from A to 2. So, Cantor's theorem is equivalent to the non{existence of a surjection A ! 2A. Putting it another way, Cantor's theorem says that for any function f : A × A ! 2 there exists a function g : A ! 2 which is not representable by f (at any member of A). In this new setting, Cantor's proof goes as follows: let 4A : A ! A × A be the diagonal function of A (4A(x) = hx; xi) and let α : 2 ! 2 be a fixed function. Define g : A ! 2 by g(x) = α(f(4A(x))). If g is representable by f and fixed a 2 A then f(a; a) = g(a) = α(f(a; a)), which shows that α has a fixed–point (namely, f(a; a)). So, for reaching to a contradiction, we need to take a function α : 2 ! 2 which does not have any fixed–point; and the only such function (without any fixed–point) is the negation function neg : 2 ! 2, neg(i) = 1 − i for i = 0; 1. For a function F : A ! P(A) let f : A × A ! 2 be defined as 1 if a 2 F (a0) f(a; a0) = 0 if a 62 F (a0) The function g constructed by the diagram f A × A - 2 6 4A neg ? A - 2 g is the characteristic function of the set DF = fx 2 A j x 62 F (x)g. That g is not representable by f (at any a 2 A) is equivalent to saying that the set DF is not in the range of F (i.e., DF 6= F (a) for any a 2 A).
Load more

Recommended publications
  • REFERENCE in ARITHMETIC §1. to Prove His Famous First
    REFERENCE IN ARITHMETIC LAVINIA PICOLLO Abstract. Self-reference has played a prominent role in the development of metamath- ematics in the past century, starting with G¨odel'sfirst incompleteness theorem. Given the nature of this and other results in the area, the informal understanding of self-reference in arithmetic has sufficed so far. Recently, however, it has been argued that for other related issues in metamathematics and philosophical logic a precise notion of self-reference and, more generally, reference, is actually required. These notions have been so far elusive and are surrounded by an aura of scepticism that has kept most philosophers away. In this paper I suggest we shouldn't give up all hope. First, I introduce the reader to these issues. Second, I discuss the conditions a good notion of reference in arithmetic must satisfy. Accordingly, I then introduce adequate notions of reference for the language of first-order arithmetic, which I show to be fruitful for addressing the aforementioned issues in metamathematics. x1. To prove his famous first incompleteness result for arithmetic, G¨odel[5] developed a technique called \arithmetization" or “g¨odelization".It consists in codifying the expressions of the language of arithmetic with numbers, so that the language can `talk' about its own formulae. Then, he constructed a sentence in the language that he described as stating its own unprovability in a system satisfying certain conditions,1 and showed this sentence to be undecidable in the system. His method led to enormous progress in metamathematics and computer science, but also in philosophical logic and other areas of philosophy where formal methods became popular.
    [Show full text]
  • The Logic of Provability
    The Logic of Provability Notes by R.J. Buehler Based on The Logic of Provability by George Boolos September 16, 2014 ii Contents Preface v 1 GL and Modal Logic1 1.1 Introduction..........................................1 1.2 Natural Deduction......................................2 1.2.1 ...........................................2 1.2.2 3 ...........................................2 1.3 Definitions and Terms....................................3 1.4 Normality...........................................4 1.5 Refining The System.....................................6 2 Peano Arithmetic 9 2.1 Introduction..........................................9 2.2 Basic Model Theory..................................... 10 2.3 The Theorems of PA..................................... 10 2.3.1 P-Terms........................................ 10 2.3.2Σ,Π, and∆ Formulas................................ 11 2.3.3 G¨odelNumbering................................... 12 2.3.4 Bew(x)........................................ 12 2.4 On the Choice of PA..................................... 13 3 The Box as Bew(x) 15 3.1 Realizations and Translations................................ 15 3.2 The Generalized Diagonal Lemma............................. 16 3.3 L¨ob'sTheorem........................................ 17 3.4 K4LR............................................. 19 3.5 The Box as Provability.................................... 20 3.6 GLS.............................................. 21 4 Model Theory for GL 23 5 Completeness & Decidability of GL 25 6 Canonical Models 27 7 On
    [Show full text]
  • Gödel's Incompleteness Theorem for Mathematicians
    G¨odel'sIncompleteness Theorem for Mathematicians Burak Kaya METU [email protected] November 23, 2016 Burak Kaya (METU) METU Math Club Student Seminars November 23, 2016 1 / 21 Hilbert wanted to formalize all mathematics in an axiomatic system which is consistent, i.e. no contradiction can be obtained from the axioms. complete, i.e. every true statement can be proved from the axioms. decidable, i.e. given a mathematical statement, there should be a procedure for deciding its truth or falsity. In 1931, Kurt G¨odelproved his famous incompleteness theorems and showed that Hilbert's program cannot be achieved. In 1936, Alan Turing proved that Hilbert's Entscheindungsproblem cannot be solved, i.e. there is no general algorithm which will decide whether a given mathematical statement is provable (from a given set of axioms.) Hilbert's program In 1920's, David Hilbert proposed a research program in the foundations of mathematics to provide secure foundations to mathematics and to eliminate the paradoxes and inconsistencies discovered by then. Burak Kaya (METU) METU Math Club Student Seminars November 23, 2016 2 / 21 consistent, i.e. no contradiction can be obtained from the axioms. complete, i.e. every true statement can be proved from the axioms. decidable, i.e. given a mathematical statement, there should be a procedure for deciding its truth or falsity. In 1931, Kurt G¨odelproved his famous incompleteness theorems and showed that Hilbert's program cannot be achieved. In 1936, Alan Turing proved that Hilbert's Entscheindungsproblem cannot be solved, i.e. there is no general algorithm which will decide whether a given mathematical statement is provable (from a given set of axioms.) Hilbert's program In 1920's, David Hilbert proposed a research program in the foundations of mathematics to provide secure foundations to mathematics and to eliminate the paradoxes and inconsistencies discovered by then.
    [Show full text]
  • Notes on Incompleteness Theorems
    The Incompleteness Theorems ● Here are some fundamental philosophical questions with mathematical answers: ○ (1) Is there a (recursive) algorithm for deciding whether an arbitrary sentence in the language of first-order arithmetic is true? ○ (2) Is there an algorithm for deciding whether an arbitrary sentence in the language of first-order arithmetic is a theorem of Peano or Robinson Arithmetic? ○ (3) Is there an algorithm for deciding whether an arbitrary sentence in the language of first-order arithmetic is a theorem of pure (first-order) logic? ○ (4) Is there a complete (even if not recursive) recursively axiomatizable theory in the language of first-order arithmetic? ○ (5) Is there a recursively axiomatizable sub-theory of Peano Arithmetic that proves the consistency of Peano Arithmetic (even if it leaves other questions undecided)? ○ (6) Is there a formula of arithmetic that defines arithmetic truth in the standard model, N (even if it does not represent it)? ○ (7) Is the (non-recursively enumerable) set of truths in the language of first-order arithmetic categorical? If not, is it ω-categorical (i.e., categorical in models of cardinality ω)? ● Questions (1) -- (7) turn out to be linked. Their philosophical interest depends partly on the following philosophical thesis, of which we will make frequent, but inessential, use. ○ Church-Turing Thesis:A function is (intuitively) computable if/f it is recursive. ■ Church: “[T]he notion of an effectively calculable function of positive integers should be identified with that of recursive function (quoted in Epstein & Carnielli, 223).” ○ Note: Since a function is recursive if/f it is Turing computable, the Church-Turing Thesis also implies that a function is computable if/f it is Turing computable.
    [Show full text]
  • Arxiv:2009.00315V2 [Math.LO] 15 Sep 2020 Tarski's Undefinability Theorem and Diagonal Lemma
    Tarski’s Undefinability Theorem and Diagonal Lemma SAEED SALEHI Research Institute for Fundamental Sciences (RIFS), University of Tabriz, P.O.Box 51666–16471, Tabriz, IRAN. E-mail:[email protected] Abstract We prove the equivalence of the semantic version of Tarski’s theorem on the undefinability of truth with a semantic version of the Diagonal Lemma, and also show the equivalence of syntactic Tarski’s Undefinability Theorem with a weak syntactic diagonal lemma. We outline two seemingly diagonal-free proofs for these theorems from the literature, and show that syntactic Tarski’s theorem can deliver G¨odel-Rosser’s Incompleteness Theorem. Keywords: Diagonal Lemma, Diagonal-Free Proofs, G¨odels Incomplteness Theorem, Rossers Theorem, Self-Reference, Tarskis Undefinability Theorem. 2020 AMS MSC: 03F40, 03A05, 03F30, 03C40. 1 Introduction ONE OF THE CORNERSTONES of modern logic (and theory of incompleteness after G¨odel) is the Diagonal Lemma (aka Self-Reference, or Fixed-Point Lemma) due to G¨odel and Carnap (see [10] and the references therein). The lemma states that (when α 7→ pαq is a suitable G¨odel coding which assigns the closed term pαq to a syntactic expression or object α) for a given formula Ψ(x) with the only free variable x, there exists some sentence θ such that the equivalence Ψ(pθq) ↔ θ holds; “holding” could mean either being true in the standard model of natural numbers N or being provable in a suitable theory T (which is usually taken to be a consistent extension of Robinson’s arithmetic). When the equivalence Ψ(pθq) ↔ θ holds in N we call it the Semantic Diagonal Lemma (studied in Section 2); when T proves the equivalence, we call it the Syntactic Diagonal Lemma.
    [Show full text]
  • Kurt Gödel Metamathematical Results on Formally Undecidable Propositions: Completeness Vs
    Kurt Gödel Metamathematical results on formally undecidable propositions: Completeness vs. Incompleteness Motto: The delight in seeing and comprehending is the most beautiful gift of nature. (A.Einstein) 1. Life and work1 Kurt Gödel was a solitary genius, whose work influenced all the subsequent developments in mathematics and logic. The striking fundamental results in the decade 1929-1939 that made Gödel famous are the completeness of the first-order predicate logic proof calculus, the incompleteness of axiomatic theories containing arithmetic, and the consistency of the axiom of choice and the continuum hypothesis with the other axioms of set theory. During the same decade Gödel made other contributions to logic, including work on intuitionism and computability, and later, under the influence of his friendship with Einstein, made a fundamental contribution to the theory of space-time. In this article I am going to summarize the most outstanding results on incompleteness and undecidability that changed the fundamental views of modern mathematics. Kurt Friedrich Gödel was born 28 April 1906, the second son of Rudolf and Marianne (Handschuh) Gödel, in Brno, Pekařská 5,2 in Moravia, at that time the Austrio-Hungarian province, now a part of the Czech Republic. This region had a mixed population that was predominantly Czech with a substantial German-speaking minority, to which Gödel’s parents belonged. Following the religion of his mother rather than his “old-catholic” father, the Gödels had Kurt baptized in the Lutheran church. In 1912, at the age of six, he was enrolled in the Evangelische Volksschule, a Lutheran school in Brno. Gödel’s ethnic patrimony is neither Czech nor Jewish, as is sometimes believed.
    [Show full text]
  • DEFINABILITY and UNDEFINABILITY of TRUTH1 Review Paper
    KRITiKA DEFINABILITY AND UNDEFINABILITY OF TRUTH1 review paper Tomislav KARAČIĆ Master of Logic Programme Institute for Logic, Language and Computation University of Amsterdam e-mail: [email protected] Abstract This thesis will focus on Tarski’s work, so the Section 2 starts with him, giving an overview of the elements of his theory of truth, leading to a presentation of his theorem in 2.3. In the rest of the paper, proposals for solving the problem of internalization of the concept of truth and the paradoxes arising from this problem with some of the proposed solution are considered. Section 3. will quickly introduce the Liar paradox and once more explicitly state Tarski’s solution, followed by the so called “revenge of the liar”; a liar-type sentence which cannot be avoided even by using Tarski’s solution to the original liar. After that, Section 4. will introduce Kripke’s Theory of Truth and his take on truth and solving the Liar paradox using paracomplete logic, while Section 5. will examine some further attempts in answering the aforementioned problems in the context of paraconsistent logic. Key words truth, Tarski's theorem, semantical paradoxes, liar, formal semantics 1 Ovaj rad pisan je kao završni rad na Odsjeku za filozofiju Hrvatskih studija u Zagrebu za potrebe ostvarivanja prvostupništva na studiju filozofije. 28 Tomislav KARAČIĆ 1. Tarski’s Theory of Truth 1.1. Importance of Tarski’s Work for Semantics During the early 20th century, among the philosophers who were driven in their work by the virtues promoted by the empiricist project, it was not uncommon to approach the concept of truth with a high dose of scepticism [13, p.
    [Show full text]
  • A Mechanised Proof of Gödel's Incompleteness Theorems Using
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Apollo A Mechanised Proof of G¨odel'sIncompleteness Theorems using Nominal Isabelle Lawrence C. Paulson Abstract An Isabelle/HOL formalisation of G¨odel'stwo incompleteness theorems is presented. The work follows Swierczkowski's´ detailed proof of the theorems using hered- itarily finite (HF) set theory [32]. Avoiding the usual arithmetical encodings of syntax eliminates the necessity to formalise elementary number theory within an embedded logical calculus. The Isabelle formalisation uses two separate treatments of variable binding: the nominal package [34] is shown to scale to a development of this complex- ity, while de Bruijn indices [3] turn out to be ideal for coding syntax. Critical details of the Isabelle proof are described, in particular gaps and errors found in the literature. 1 Introduction This paper describes mechanised proofs of G¨odel'sincompleteness theorems [8], includ- ing the first mechanised proof of the second incompleteness theorem. Very informally, these results can be stated as follows: Theorem 1 (First Incompleteness Theorem) If L is a consistent theory capable of formalising a sufficient amount of elementary mathematics, then there is a sentence δ such that neither δ nor :δ is a theorem of L, and moreover, δ is true.1 Theorem 2 (Second Incompleteness Theorem) If L is as above and Con(L) is a sentence stating that L is consistent, then Con(L) is not a theorem of L. Both of these will be presented formally below. Let us start to examine what these theorems actually assert.
    [Show full text]
  • SELF-REFERENCE in ARITHMETIC I VOLKER HALBACH Oxford University and ALBERT VISSER Utrecht University
    THE REVIEW OF SYMBOLIC LOGIC Volume 7, Number 4, December 2014 SELF-REFERENCE IN ARITHMETIC I VOLKER HALBACH Oxford University and ALBERT VISSER Utrecht University The net result is to substitute articulate hesitation for inarticulate certainty. Whether this result has any value is a question which I shall not consider. Russell (1940, p. 11) Abstract. A Gödel sentence is often described as a sentence saying about itself that it is not provable, and a Henkin sentence as a sentence stating its own provability. We discuss what it could mean for a sentence of arithmetic to ascribe to itself a property such as provability or unprov- ability. The starting point will be the answer Kreisel gave to Henkin’s problem. We describe how the properties of the supposedly self-referential sentences depend on the chosen coding, the formulae expressing the properties and the way a fixed points for the formulae are obtained. This paper is the first of two papers. In the present paper we focus on provability. In part II, we will consider other properties like Rosser provability and partial truth predicates. §1. Introduction. ‘We thus have a sentence before us that states its own unprovability.’ This is how Gödel describes the kind of sentence that has come to bear his name.1 Ever since, sentences constructed by Gödel’s method have been described in lectures and logic textbooks as saying about themselves that they are not provable or as ascribing to them- selves the property of being unprovable. The only ‘self–reference–like’ feature of the Gödel sentence γ that is used in the usual modern proofs of Gödel’s first incompleteness theorem is the derivability of the equiv- alence γ ↔¬Bew(γ); in other words, the only feature needed is the fact that γ is a (provable) fixed point of ¬Bew(x).2 But the fact that a sentence is a fixed point of a certain formula expressing a certain property does by no means guarantee that the sentence ascribes that property to itself, as we shall argue in what follows; and whether γ is also Received: Dec.
    [Show full text]
  • Instructor's Manual Computability and Logic
    INSTRUCTOR’S MANUAL FOR COMPUTABILITY AND LOGIC FIFTH EDITION PART A. FOR ALL READERS JOHN P. BURGESS Professor of Philosophy Princeton University [email protected] Note This work is subject to copyright, but instructors who adopt Computability & Logic as a textbook are hereby authorized to copy and distribute the present Part A. This permission does not extend to Part B. Contents Dependence of Chapters (Leitfaden) 2 General Remarks on Problems (for Students) 3 Hints for Odd-Numbered Problems Computability Theory 4 Hints for Odd-Numbered Problems Basic Metalogic 11 Errata 20 2 3 Dependence of Chapters 4 General Remarks on Problems (for Students) • The problems for each chapter should be read as part of that chapter, even those that are not assigned. They often add important information not covered in the text. • The results of earlier problems, whether or not assigned, may be used in later problems. Many problems are parts of sequences. • Before working the problems for any chapter, check to see whether there are any errata listed for that chapter, and especially for its problems. • Hints are provided for odd-numbered problems in chapters 1-18. The hints for some problems are inevitably more substantial than those for others. 5 Hints for Odd-Numbered Problems: Computability Theory (Chapters 1-8) Chapter 1 1.1 The converse assertion then follows from the first assertion by applying it to f -1 and its inverse f -1-1. 1.3 For (a) consider the identity function i(a) = a for all a in A. For (b) and (c) use the preceding two problems, as per the general hint above.
    [Show full text]
  • Gödel Incompleteness Revisited Grégory Lafitte
    Gödel incompleteness revisited Grégory Lafitte To cite this version: Grégory Lafitte. Gödel incompleteness revisited. JAC 2008, Apr 2008, Uzès, France. pp.74-89. hal-00274564 HAL Id: hal-00274564 https://hal.archives-ouvertes.fr/hal-00274564 Submitted on 18 Apr 2008 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. Journees´ Automates Cellulaires 2008 (Uzes),` pp. 74-89 GODEL¨ INCOMPLETENESS REVISITED GREGORY LAFITTE 1 1 Laboratoire d’Informatique Fondamentale de Marseille (LIF), CNRS – Aix-Marseille Universit´e, 39 rue Joliot-Curie, 13453 Marseille Cedex 13, France E-mail address: [email protected] URL: http://www.lif.univ-mrs.fr/~lafitte/ Abstract. We investigate the frontline of G¨odel’sincompleteness theorems’ proofs and the links with computability. The G¨odelincompleteness phenomenon G¨odel’sincompleteness theorems [G¨od31,SFKM+86] are milestones in the subject of mathematical logic. Apart from G¨odel’soriginal syntactical proof, many other proofs have been presented. Kreisel’s proof [Kre68] was the first with a model-theoretical flavor. Most of these proofs are attempts to get rid of any form of self-referential reasoning, even if there remains diagonalization arguments in each of these proofs.
    [Show full text]
  • Diagonalization in Formal Mathematics
    Paulo Guilherme Domingos Canha Moreira dos Santos Bachelor in Mathematics Diagonalization in Formal Mathematics Dissertation submitted in partial fulfillment of the requirements for the degree of Master of Science in Mathematics and Applications Adviser: Prof. Isabel Oitavem, Associate Professor, NOVA University of Lisbon Co-adviser: Prof. Reinhard Kahle, Full Professor, NOVA University of Lisbon Examination Committee Chair: Prof. João Jorge Ribeiro Soares Gonçalves de Araújo Rapporteur: Prof. Gilda Maria Saraiva Dias Ferreira Member: Prof. Reinhard Josef Klaus Kahle March, 2019 Diagonalization in Formal Mathematics Copyright © Paulo Guilherme Domingos Canha Moreira dos Santos, Faculty of Sciences and Technology, NOVA University Lisbon. The Faculty of Sciences and Technology and the NOVA University Lisbon have the right, perpetual and without geographical boundaries, to file and publish this dissertation through printed copies reproduced on paper or on digital form, or by any other means known or that may be invented, and to disseminate through scientific repositories and admit its copying and distribution for non-commercial, educational or research purposes, as long as credit is given to the author and editor. This document was created using the (pdf)LATEX processor, based on the “novathesis” template[1], developed at the Dep. Informática of FCT-NOVA [2]. [1] https://github.com/joaomlourenco/novathesis [2] http://www.di.fct.unl.pt A todos aqueles que me ajudaram a ser quem sou, que me ajudaram a sonhar mais alto e a nunca desistir, e que me ensinaram a ser feliz. Aos meus pais: José Paulo e Isabel. Aos meus avós: Adriana, Guilherme, Carminda e António. À Pi. Acknowledgements I am very thankful to my Advisers — Professor Isabel Oitavem and Professor Reinhard Kahle — for their help for the work developed in the current thesis.
    [Show full text]