Intuitionistic Logic
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On Proof Interpretations and Linear Logic
On Proof Interpretations and Linear Logic On Proof Interpretations and Linear Logic Paulo Oliva Queen Mary, University of London, UK ([email protected]) Heyting Day Utrecht, 27 February 2015 To Anne Troelstra and Dick de Jongh 6 ?? - !A ::: - !A - ! ILLp ILLp ILLp = Intuit. predicate linear logic (!-free) On Proof Interpretations and Linear Logic Overview - ! IL ::: - IL interpretations IL = Intuitionistic predicate logic 6 ?? - !A ::: - !A On Proof Interpretations and Linear Logic Overview - ! IL ::: - IL interpretations - ! ILLp ILLp IL = Intuitionistic predicate logic ILLp = Intuit. predicate linear logic (!-free) ?? - !A ::: - !A On Proof Interpretations and Linear Logic Overview - ! IL ::: - IL interpretations 6 - ! ILLp ILLp IL = Intuitionistic predicate logic ILLp = Intuit. predicate linear logic (!-free) - !A ::: - !A On Proof Interpretations and Linear Logic Overview - ! IL ::: - IL interpretations 6 ?? - ! ILLp ILLp IL = Intuitionistic predicate logic ILLp = Intuit. predicate linear logic (!-free) On Proof Interpretations and Linear Logic Overview - ! IL ::: - IL interpretations 6 ?? - ! ILLp ILLp - !A ::: - !A IL = Intuitionistic predicate logic ILLp = Intuit. predicate linear logic (!-free) On Proof Interpretations and Linear Logic Outline 1 Proof Interpretations 2 Linear Logic 3 Unified Interpretation of Linear Logic On Proof Interpretations and Linear Logic Proof Interpretations Outline 1 Proof Interpretations 2 Linear Logic 3 Unified Interpretation of Linear Logic E.g. the set of prime numbers is infinite The book \Proofs from THE BOOK" contains six beautiful proofs of this Non-theorems map to the empty set E.g. the set of even numbers is finite Need to fix the formal system On Proof Interpretations and Linear Logic Proof Interpretations Formulas as Sets of Proofs Formulas as set of proofs A 7! fπ : π ` Ag The book \Proofs from THE BOOK" contains six beautiful proofs of this Non-theorems map to the empty set E.g. -
The Logic of Brouwer and Heyting
THE LOGIC OF BROUWER AND HEYTING Joan Rand Moschovakis Intuitionistic logic consists of the principles of reasoning which were used in- formally by L. E. J. Brouwer, formalized by A. Heyting (also partially by V. Glivenko), interpreted by A. Kolmogorov, and studied by G. Gentzen and K. G¨odel during the first third of the twentieth century. Formally, intuitionistic first- order predicate logic is a proper subsystem of classical logic, obtained by replacing the law of excluded middle A ∨¬A by ¬A ⊃ (A ⊃ B); it has infinitely many dis- tinct consistent axiomatic extensions, each necessarily contained in classical logic (which is axiomatically complete). However, intuitionistic second-order logic is inconsistent with classical second-order logic. In terms of expressibility, the intu- itionistic logic and language are richer than the classical; as G¨odel and Gentzen showed, classical first-order arithmetic can be faithfully translated into the nega- tive fragment of intuitionistic arithmetic, establishing proof-theoretical equivalence and clarifying the distinction between the classical and constructive consequences of mathematical axioms. The logic of Brouwer and Heyting is effective. The conclusion of an intuitionistic derivation holds with the same degree of constructivity as the premises. Any proof of a disjunction of two statements can be effectively transformed into a proof of one of the disjuncts, while any proof of an existential statement contains an effec- tive prescription for finding a witness. The negation of a statement is interpreted as asserting that the statement is not merely false but absurd, i.e., leads to a contradiction. Brouwer objected to the general law of excluded middle as claim- ing a priori that every mathematical problem has a solution, and to the general law ¬¬A ⊃ A of double negation as asserting that every consistent mathematical statement holds. -
Finite Type Arithmetic
Finite Type Arithmetic Computable Existence Analysed by Modified Realisability and Functional Interpretation H Klaus Frovin Jørgensen Master’s Thesis, March 19, 2001 Supervisors: Ulrich Kohlenbach and Stig Andur Pedersen Departments of Mathematics and Philosohy University of Roskilde Abstract in English and Danish Motivated by David Hilbert’s program and philosophy of mathematics we give in the context of natural deduction an introduction to the Dialectica interpretation and compare the interpre- tation with modified realisability. We show how the interpretations represent two structurally different methods for unwinding computable information from proofs which may use certain prima facie non-constructive (ideal) elements of mathematics. Consequently, the two inter- pretations also represent different views on what is to be regarded as constructive relative to arithmetic. The differences show up in the interpretations of extensionality, Markov’s prin- ciple and restricted forms of independence-of-premise. We show that it is computationally a subtle issue to combine these ideal elements and prove that Markov’s principle is computa- tionally incompatible with independence-of-premise for negated purely universal formulas. In the context of extracting computational content from proofs in typed classical arith- metic we also compare in an extensional context (i) the method provided by negative trans- lation + Dialectica interpretation with (ii) the method provided by negative translation + ω A-translation + modified realisability. None of these methods can be applied fully to E-PA , since E-HAω is not closed under Markov’s rule, whereas the method based on the Dialectica interpretation can be used if only weak extensionality is required. Finally, we present a new variant of the Dialectica interpretation in order to obtain (the well-known) existence property, disjunction property and other closure results for typed in- tuitionistic arithmetic and extensions hereof. -
Epistemic Modality, Mind, and Mathematics
Epistemic Modality, Mind, and Mathematics Hasen Khudairi June 20, 2017 c Hasen Khudairi 2017, 2020 All rights reserved. 1 Abstract This book concerns the foundations of epistemic modality. I examine the nature of epistemic modality, when the modal operator is interpreted as con- cerning both apriority and conceivability, as well as states of knowledge and belief. The book demonstrates how epistemic modality relates to the compu- tational theory of mind; metaphysical modality; deontic modality; the types of mathematical modality; to the epistemic status of undecidable proposi- tions and abstraction principles in the philosophy of mathematics; to the apriori-aposteriori distinction; to the modal profile of rational propositional intuition; and to the types of intention, when the latter is interpreted as a modal mental state. Each essay is informed by either epistemic logic, modal and cylindric algebra or coalgebra, intensional semantics or hyperin- tensional semantics. The book’s original contributions include theories of: (i) epistemic modal algebras and coalgebras; (ii) cognitivism about epistemic modality; (iii) two-dimensional truthmaker semantics, and interpretations thereof; (iv) the ground-theoretic ontology of consciousness; (v) fixed-points in vagueness; (vi) the modal foundations of mathematical platonism; (vii) a solution to the Julius Caesar problem based on metaphysical definitions availing of notions of ground and essence; (viii) the application of epistemic two-dimensional semantics to the epistemology of mathematics; and (ix) a modal logic for rational intuition. I develop, further, a novel approach to conditions of self-knowledge in the setting of the modal µ-calculus, as well as novel epistemicist solutions to Curry’s and the liar paradoxes. -
The Consistency of Arithmetic
The Consistency of Arithmetic Timothy Y. Chow July 11, 2018 In 2010, Vladimir Voevodsky, a Fields Medalist and a professor at the Insti- tute for Advanced Study, gave a lecture entitled, “What If Current Foundations of Mathematics Are Inconsistent?” Voevodsky invited the audience to consider seriously the possibility that first-order Peano arithmetic (or PA for short) was inconsistent. He briefly discussed two of the standard proofs of the consistency of PA (about which we will say more later), and explained why he did not find either of them convincing. He then said that he was seriously suspicious that an inconsistency in PA might someday be found. About one year later, Voevodsky might have felt vindicated when Edward Nelson, a professor of mathematics at Princeton University, announced that he had a proof not only that PA was inconsistent, but that a small fragment of primitive recursive arithmetic (PRA)—a system that is widely regarded as implementing a very modest and “safe” subset of mathematical reasoning—was inconsistent [11]. However, a fatal error in his proof was soon detected by Daniel Tausk and (independently) Terence Tao. Nelson withdrew his claim, remarking that the consistency of PA remained “an open problem.” For mathematicians without much training in formal logic, these claims by Voevodsky and Nelson may seem bewildering. While the consistency of some axioms of infinite set theory might be debatable, is the consistency of PA really “an open problem,” as Nelson claimed? Are the existing proofs of the con- sistency of PA suspect, as Voevodsky claimed? If so, does this mean that we cannot be sure that even basic mathematical reasoning is consistent? This article is an expanded version of an answer that I posted on the Math- Overflow website in response to the question, “Is PA consistent? do we know arXiv:1807.05641v1 [math.LO] 16 Jul 2018 it?” Since the question of the consistency of PA seems to come up repeat- edly, and continues to generate confusion, a more extended discussion seems worthwhile. -
Subverting the Classical Picture: (Co)Algebra, Constructivity and Modalities∗
Informatik 8, FAU Erlangen-Nürnberg [email protected] Subverting the Classical Picture: (Co)algebra, Constructivity and Modalities∗ Tadeusz Litak Contents 1. Subverting the Classical Picture 2 2. Beyond Frege and Russell: Modalities Instead of Predicates 6 3. Beyond Peirce, Tarski and Kripke: Coalgebras and CPL 11 3.1. Introduction to the Coalgebraic Framework ............. 11 3.2. Coalgebraic Predicate Logic ...................... 14 4. Beyond Cantor: Effectivity, Computability and Determinacy 16 4.1. Finite vs. Classical Model Theory: The Case of CPL ........ 17 4.2. Effectivity, Choice and Determinacy in Formal Economics ..... 19 4.3. Quasiconstructivity and Modal Logic ................. 21 5. Beyond Scott, Montague and Moss: Algebras and Possibilities 23 5.1. Dual Algebras, Neighbourhood Frames and CA-baes ........ 23 5.2. A Hierachy of (In)completeness Notions for Normal Modal Logics . 24 5.3. Possibility Semantics and Complete Additivity ........... 26 5.4. GQM: One Modal Logic to Rule Them All? ............. 28 6. Beyond Boole and Lewis: Intuitionistic Modal Logic 30 6.1. Curry-Howard Correspondence, Constructive Logic and 2 ..... 31 6.2. Guarded Recursion and Its Neighbours ................ 33 6.3. KM, mHC, LC and the Topos of Trees ................ 34 6.4. Between Boole and Heyting: Negative Translations ......... 35 7. Unifying Lewis and Brouwer 37 7.1. Constructive Strict Implication .................... 37 7.2. Relevance, Resources and (G)BI .................... 40 ∗Introductory overview chapter for my cumulative habilitation thesis as required by FAU Erlangen-Nürnberg regulations (submitted in 2018, finally approved in May 2019). Available online at https://www8.cs.fau. de/ext/litak/gitpipe/tadeusz_habilitation.pdf. 1 8. Beyond Brouwer, Heyting and Kolmogorov: Nondistributivity 43 8.1. -
The Unintended Interpretations of Intuitionistic Logic
THE UNINTENDED INTERPRETATIONS OF INTUITIONISTIC LOGIC Wim Ruitenburg Department of Mathematics, Statistics and Computer Science Marquette University Milwaukee, WI 53233 Abstract. We present an overview of the unintended interpretations of intuitionis- tic logic that arose after Heyting formalized the “observed regularities” in the use of formal parts of language, in particular, first-order logic and Heyting Arithmetic. We include unintended interpretations of some mild variations on “official” intuitionism, such as intuitionistic type theories with full comprehension and higher order logic without choice principles or not satisfying the right choice sequence properties. We conclude with remarks on the quest for a correct interpretation of intuitionistic logic. §1. The Origins of Intuitionistic Logic Intuitionism was more than twenty years old before A. Heyting produced the first complete axiomatizations for intuitionistic propositional and predicate logic: according to L. E. J. Brouwer, the founder of intuitionism, logic is secondary to mathematics. Some of Brouwer’s papers even suggest that formalization cannot be useful to intuitionism. One may wonder, then, whether intuitionistic logic should itself be regarded as an unintended interpretation of intuitionistic mathematics. I will not discuss Brouwer’s ideas in detail (on this, see [Brouwer 1975], [Hey- ting 1934, 1956]), but some aspects of his philosophy need to be highlighted here. According to Brouwer mathematics is an activity of the human mind, a product of languageless thought. One cannot be certain that language is a perfect reflection of this mental activity. This makes language an uncertain medium (see [van Stigt 1982] for more details on Brouwer’s ideas about language). In “De onbetrouwbaarheid der logische principes” ([Brouwer 1981], pp. -
Intuitionistic Three-Valued Logic and Logic Programming Informatique Théorique Et Applications, Tome 25, No 6 (1991), P
INFORMATIQUE THÉORIQUE ET APPLICATIONS J. VAUZEILLES A. STRAUSS Intuitionistic three-valued logic and logic programming Informatique théorique et applications, tome 25, no 6 (1991), p. 557-587 <http://www.numdam.org/item?id=ITA_1991__25_6_557_0> © AFCET, 1991, tous droits réservés. L’accès aux archives de la revue « Informatique théorique et applications » im- plique l’accord avec les conditions générales d’utilisation (http://www.numdam. org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/ Informatique théorique et Applications/Theoretical Informaties and Applications (vol. 25, n° 6, 1991, p. 557 à 587) INTUITIONISTIC THREE-VALUED LOGIC AMD LOGIC PROGRAMM1NG (*) by J. VAUZEILLES (*) and A. STRAUSS (2) Communicated by J. E. PIN Abstract. - In this paper, we study the semantics of logic programs with the help of trivalued hgic, introduced by Girard in 1973. Trivalued sequent calculus enables to extend easily the results of classical SLD-resolution to trivalued logic. Moreover, if one allows négation in the head and in the body of Hom clauses, one obtains a natural semantics for such programs regarding these clauses as axioms of a theory written in the intuitionistic fragment of that logic. Finally^ we define in the same calculus an intuitionistic trivalued version of Clark's completion, which gives us a déclarative semantics for programs with négation in the body of the clauses, the évaluation method being SLDNF-resolution. Resumé. — Dans cet article, nous étudions la sémantique des programmes logiques à l'aide de la logique trivaluée^ introduite par Girard en 1973. -
Introduction to Formal Logic II (3 Credit
PHILOSOPHY 115 INTRODUCTION TO FORMAL LOGIC II BULLETIN INFORMATION PHIL 115 – Introduction to Formal Logic II (3 credit hrs) Course Description: Intermediate topics in predicate logic, including second-order predicate logic; meta-theory, including soundness and completeness; introduction to non-classical logic. SAMPLE COURSE OVERVIEW Building on the material from PHIL 114, this course introduces new topics in logic and applies them to both propositional and first-order predicate logic. These topics include argument by induction, duality, compactness, and others. We will carefully prove important meta-logical results, including soundness and completeness for both propositional logic and first-order predicate logic. We will also learn a new system of proof, the Gentzen-calculus, and explore first-order predicate logic with functions and identity. Finally, we will discuss potential motivations for alternatives to classical logic, and examine how those motivations lead to the development of intuitionistic logic, including a formal system for intuitionistic logic, comparing the features of that formal system to those of classical first-order predicate logic. ITEMIZED LEARNING OUTCOMES Upon successful completion of PHIL 115, students will be able to: 1. Apply, as appropriate, principles of analytical reasoning, using as a foundation the knowledge of mathematical, logical, and algorithmic principles 2. Recognize and use connections among mathematical, logical, and algorithmic methods across disciplines 3. Identify and describe problems using formal symbolic methods and assess the appropriateness of these methods for the available data 4. Effectively communicate the results of such analytical reasoning and problem solving 5. Explain and apply important concepts from first-order logic, including duality, compactness, soundness, and completeness 6. -
The Proper Explanation of Intuitionistic Logic: on Brouwer's Demonstration
The proper explanation of intuitionistic logic: on Brouwer’s demonstration of the Bar Theorem Göran Sundholm, Mark van Atten To cite this version: Göran Sundholm, Mark van Atten. The proper explanation of intuitionistic logic: on Brouwer’s demonstration of the Bar Theorem. van Atten, Mark Heinzmann, Gerhard Boldini, Pascal Bourdeau, Michel. One Hundred Years of Intuitionism (1907-2007). The Cerisy Conference, Birkhäuser, pp.60- 77, 2008, 978-3-7643-8652-8. halshs-00791550 HAL Id: halshs-00791550 https://halshs.archives-ouvertes.fr/halshs-00791550 Submitted on 24 Jan 2017 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. Distributed under a Creative Commons Attribution - NonCommercial| 4.0 International License The proper explanation of intuitionistic logic: on Brouwer’s demonstration of the Bar Theorem Göran Sundholm Philosophical Institute, Leiden University, P.O. Box 2315, 2300 RA Leiden, The Netherlands. [email protected] Mark van Atten SND (CNRS / Paris IV), 1 rue Victor Cousin, 75005 Paris, France. [email protected] Der … geführte Beweis scheint mir aber trotzdem . Basel: Birkhäuser, 2008, 60–77. wegen der in seinem Gedankengange enthaltenen Aussagen Interesse zu besitzen. (Brouwer 1927B, n. 7)1 Brouwer’s demonstration of his Bar Theorem gives rise to provocative ques- tions regarding the proper explanation of the logical connectives within intu- itionistic and constructivist frameworks, respectively, and, more generally, re- garding the role of logic within intuitionism. -
On the Intermediate Logic of Open Subsets of Metric Spaces Timofei Shatrov
On the intermediate logic of open subsets of metric spaces Timofei Shatrov abstract. In this paper we study the intermediate logic MLO( ) of open subsets of a metric space . This logic is closely related to Medvedev’sX logic X of finite problems ML. We prove several facts about this logic: its inclusion in ML, impossibility of its finite axiomatization and indistinguishability from ML within some large class of propositional formulas. Keywords: intermediate logic, Medvedev’s logic, axiomatization, indistin- guishability 1 Introduction In this paper we introduce and study a new intermediate logic MLO( ), which we first define using Kripke semantics and then we will try to ratio-X nalize this definition using the concepts from prior research in this field. An (intuitionistic) Kripke frame is a partially ordered set (F, ). A Kripke model is a Kripke frame with a valuation θ (a function which≤ maps propositional variables to upward-closed subsets of the Kripke frame). The notion of a propositional formula being true at some point w F of a model M = (F,θ) is defined recursively as follows: ∈ For propositional letter p , M, w p iff w θ(p ) i i ∈ i M, w ψ χ iff M, w ψ and M, w χ ∧ M, w ψ χ iff M, w ψ or M, w χ ∨ M, w ψ χ iff for any w′ w, M, w ψ implies M, w′ χ → ≥ M, w 6 ⊥ A formula is true in a model M if it is true in each point of M. A formula is valid in a frame F if it is true in all models based on that frame. -
Consistency, Contradiction and Negation. Logic, Epistemology, and the Unity of Science Series
BOOK REVIEW: CARNIELLI, W., CONIGLIO, M. Paraconsistent Logic: Consistency, Contradiction and Negation. Logic, Epistemology, and the Unity of Science Series. (New York: Springer, 2016. ISSN: 2214-9775.) Henrique Antunes Vincenzo Ciccarelli State University of Campinas State University of Campinas Department of Philosophy Department of Philosophy Campinas, SP Campinas, SP Brazil Brazil [email protected] [email protected] Article info CDD: 160 Received: 01.12.2017; Accepted: 30.12.2017 DOI: http://dx.doi.org/10.1590/0100-6045.2018.V41N2.HV Keywords: Paraconsistent Logic LFIs ABSTRACT Review of the book 'Paraconsistent Logic: Consistency, Contradiction and Negation' (2016), by Walter Carnielli and Marcelo Coniglio The principle of explosion (also known as ex contradictione sequitur quodlibet) states that a pair of contradictory formulas entails any formula whatsoever of the relevant language and, accordingly, any theory regimented on the basis of a logic for which this principle holds (such as classical and intuitionistic logic) will turn out to be trivial if it contains a pair of theorems of the form A and ¬A (where ¬ is a negation operator). A logic is paraconsistent if it rejects the principle of explosion, allowing thus for the possibility of contradictory and yet non-trivial theories. Among the several paraconsistent logics that have been proposed in the literature, there is a particular family of (propositional and quantified) systems known as Logics of Formal Inconsistency (LFIs), developed and thoroughly studied Manuscrito – Rev. Int. Fil. Campinas, v. 41, n. 2, pp. 111-122, abr.-jun. 2018. Henrique Antunes & Vincenzo Ciccarelli 112 within the Brazilian tradition on paraconsistency. A distinguishing feature of the LFIs is that although they reject the general validity of the principle of explosion, as all other paraconsistent logics do, they admit a a restrcited version of it known as principle of gentle explosion.