DOCSLIB.ORG

Conquering the Meredith Single Axiom

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Conquering the Meredith Single Axiom Conquering the Meredith Single Axiom Larry Wos Mathematics and Computer Science Division Argonne National Lab oratory Argonne IL email wosmcsanlgov May Abstract For more than three and onehalf decades b eginning in the early s a heavy emphasis on pro of nding has b een a key comp onent of the Argonne paradigm whose use has directly led to signicant advances in automated reasoning and imp ortant con tributions to mathematics and logic The theorems that have served well range from the trivial to the deep even including some that corresp onded to op en questions Often the paradigm asks for a theorem whose pro of is in hand but that cannot b e obtained in a fully automated manner by the program in use The theorem whose hypothesis consists solely of the Meredith single axiom for twovalued sentential or prop ositional calculus and whose conclusion is the Lukasiewicz threeaxiom system for that area of formal logic was just such a theorem Featured in this article is the metho dology that enabled the program OTTER to nd the rst fully automated pro of of the cited theo rem a pro of with the intriguing prop erty that none of its steps contains a term of the form nnt for any term t As evidence of the p ower of the new metho dology the article also discusses OTTERs success in obtaining the rst known pro of of a theorem concerning a single axiom of Lukasiewicz Keywordsautomated reasoning double negation Meredith single axiom prop ositional calculus twovalued sentential calculus This work was supp orted by the Mathematical Information and Computational Sciences Division subprogram of the Oce of Advanced Scientic Computing Research US Department of Energy under Contract WEng The Original Problem For many years the Meredith single axiom for twovalued sentential or prop ositional calculus had successfully resisted a fully automated pro of Following is Merediths axiom expressed in clause notation Piiiiixyinznuzviivxiux Although the automated reasoning program OTTER McCune was sp eedily able to pro of check what amounts to the original step pro of of the Meredith single axiom no combination of strategies and parameter settings yielded a pro of that was not strongly guided by knowledge of that original pro of Note that pro of checking esp ecially when condensed detachment is the inference rule to b e used is far far easier than pro of nding their natures dier sharply Also of note Merediths original pro of in contrast to the cited step pro of was not based strictly on condensed detachment indeed his step pro of relies in part up on substitution and in part on detachment More generally b e warned that pro of length and pro of itself in the literature can b e misleading as the preceding illustrates The target chosen by Meredith and featured in the research discussed here was the Lukasiewicz threeaxiom system Lukasiewicz expressed in clause notation Piixyiiyzixz Piinxxx Pixinxy This article fo cuses on the conquering of the axiomon the formulation of a metho d ology that yields a fully automated pro of that b egins with the Meredith single axiom and completes with the deduction of the three Lukasiewicz axioms The metho dology relies in no way on knowledge of the pro of b eing sought Moreover as required by any metho dology that is to b e resp ected its use led to a distinct and startling success to b e presented here namely completion of a pro of that the Lukasiewicz letter axiom is sucient for the study of all of twovalued sentential or prop ositional calculus Before the development of the metho dology featured in this article no pro of of this single axiom was known The factors that led to the conquest and replaced the years of failure are detailed Also discussed in this article is the topic of shortening pro ofs and the resultant algo rithm I was able to formulate for making such attempts The algorithm as explained in Section is the s complement to the metho dology featured here A Burning Question Esp ecially for the individual unfamiliar with automated reasoning a natural and even burning question immediately arises Why sp end time and eort trying to nd a means for a program to prove a theorem whose pro of is readily available From a historical viewp oint the answer rests with the continued practice of the Argonne group namely rst identify a theorem whose pro of is out of reach of our current program and then wrestle with that theorem until a means is found to bring its pro of within range From the viewp oint of automated reasoning the general principle asserts that progress is quite likely to o ccur when the arsenal of weapons is augmented to p ermit the pro of of a theorem that had resisted automation Whether the theorem has already b een proved or simply conjectured to b e true is not the crucial element although the latter case pro duces more excitement One danger always exists The new approach may b e consciously or unconsciously tailored to the theorem under consideration To b e of interest and to oer the strong p ossibility that an advance has o ccurred such tailoring must b e absent Therefore the supp osed advance must b e put to the test of applying it to similar theorems or even b etter to some not so similar A number of the weapons now oered by a program such as OTTER can trace their birth to the study of a theorem whose pro of was already in hand The Key Factors Four factors app ear to account for the success to b e rep orted here in some detail First directly at the suggestion of my colleague Branden Fitelson the heat parameter was assigned the value Second a series of lemmas whose choice is in no way based on the theorem under attack was included as targets that when proved were then added to the initial set of supp ort for the next run and the pro cess was rep eated until a pro of of the desired theorem was obtained Third at some p oint all of the pro of steps of the alreadyproved lemmas even those thought to b e irrelevant to the task were adjoined as resonators Fourthand indeed counterintuitivethe goal of nding a pro of was replaced by the goal of nding a pro of totally free of double negation From what I know and from what Fitelson has found prior to the study rep orted here no such pro of for the Meredith single axiom had b een oered Before turning to the details of the metho dology I rst oer a fuller treatment of each of the four factors Turning up the Heat The rst factor fo cuses on the use of the hot list strategy Wosb My usual approach is to set the input heat parameter to a value no greater than When the theorem under attack relies on a single axiom however a value of or even greater is recommended Indeed as my colleague Fitelson p ointed out if you examine a pro of of a theorem of the type under discussion you often nd a large number of its steps have as a hypotheses the single axiom He was studying the use of condensed detachment with a heavy emphasis on the step pro of of the Meredith single axiom Moreover you also frequently nd that a sequence of such steps o ccurs consecutively with the second based on the rst the third on the second and the like The two observations taken together suggested to him that an unusually high value assigned to the input heat parameter coupled with the placement of the single axiom in the initial hot list might enable OTTER to nd such tightly connected sequences of steps For example if a retained clause C has heat if the input value is and if the initial hot list contains b oth the clause corresp onding to the single axiom and that corresp onding to condensed detachment then b efore leaving the scene C would b e used with condensed detachment and the single axiom to yield C Similarly C would b e used to deduce C assuming that C was retained and the pro cess could continue until C was deduced and retained I have found that Fitelsons analysis exhibits excellent insight Therefore I recommend assigning a value of or greater to the input heat parameter when the theorem under attack fo cuses on a single axiom Adding to the Initial Set of Supp ort The second factor concerns amending the initial set of supp ort for a subsequent run You might as I did puzzle over the value of such a move if the resonance strategy were already in use and the resonators corresp onding to the set of target lemmas were already present Indeed on the surface if one of the target lemmas was deduced say in the rst run and its resonator was already present then it would quite quickly b ecome the fo cus of attention to initiate applications of the inference rules in use Therefore how could the programs attack b e enhanced in the socalled second run by having such a lemma included in the input set of supp ort In particular the two approaches would seem to b e essentially equivalent As Fitelson and I hazarded in a phone conversation here is the probable dierence by example If the target lemma is deduced and retained rather than b eing present at the b eginning of the run at say clause and used to deduce a complex clause that is retained and given say the number then the clause numbered might never b e chosen as the fo cus of attention for inferencerule initiation Even with the presence of the ratio strategy and a value of assigned to the pick given ratio OTTER might never or almost never choose clause as the fo cus of attention On the other hand in a run in which the clause corresp onding to the target lemma numbered in the preceding comments is included in the initial set of supp ort the clause that would have b een numbered might now b e numbered or less and hence will b e chosen
Load more

Recommended publications
  • Logical Calculi 0 ✬ ✩
    Ernst, Fitelson, & Harris Some New Results in Logical Calculi 0 ✬ ✩ Some New Results in Logical Calculi Obtained Using Automated Reasoning Zac Ernst, Ken Harris & Branden Fitelson Department of Philosophy University of Wisconsin–Madison & AR @ MCS @ ANL July 13, 2001 ✫ ✪ AR @ MCS @ ANL July 13, 2000 Ernst, Fitelson, & Harris Some New Results in Logical Calculi 1 ✬ ✩ Overview of Presentation • Some Unfinished Business from Our Last Meeting – Classical Propositional Calculus in the Sheffer Stroke (D) – Classical Propositional Calculus in C and O • Some NewResults in Other Logical Calculi – NewBases for LG ( including new, shortest known single axioms) – NewBases for C5 ( including new, shortest known bases) – NewBases for C4 ( including new, shortest known single axiom) – NewBases for RM → (including new, shortest known bases) – Miscellaneous Results for E→,R→,RM→,and(L→ • Discussion of AR Techniques Used and Developed ... ✫ ✪ AR @ MCS @ ANL July 13, 2000 ✬Ernst, Fitelson, & Harris Some New Results in Logical Calculi 2✩ Sheffer Stroke Axiomatizations of Sentential Logic: I • At our last meeting, we reported some investigations into Sheffer Stroke axiomatizations of the classical propositional calculus. • In these systems, the only rule of inference is the following, somewhat odd, detachment rule for D: (D-Rule) From DpDqr and p,inferr. • Four 23-symbol single axioms have been known for many years.a (N) DDpDqrDDtDttDDsqDDpsDps ((L1) DDpDqrDDsDssDDsqDDpsDps ((L2) DDpDqrDDpDrpDDsqDDpsDps (W) DDpDqrDDDsrDDpsDpsDpDpq aThese axioms are discussed in [11], [5, pp. 179–196], and [22, pp. 37–39]. ✫ ✪ AR @ MCS @ ANL July 13, 2000 ✬Ernst, Fitelson, & Harris Some New Results in Logical Calculi 3✩ Sheffer Stroke Axiomatizations of Sentential Logic: II • As we reported last time, Ken and I were able to find many (60+) new23-symbol single axioms for this system, including: DDpDqrDDpDqrDDsrDDrsDps • Last year, we began to look for shorter single axioms.
    [Show full text]
  • Mathematical Logic and Computers Some Interesting Examples
    Introduction Classical Propositional Logic Intuitionistic Propositional Logic Double Negation Elimination Many-Valued Propositional Logic Modal Logic Conclusion Mathematical Logic and Computers Some interesting examples Michael Beeson San Jos´eState University August 28, 2008 Michael Beeson Logic and Computers Introduction Classical Propositional Logic Intuitionistic Propositional Logic Double Negation Elimination Many-Valued Propositional Logic Modal Logic Conclusion Introduction Classical Propositional Logic Various Axiomatizations Detachment and substitution Using resolution logic for a metalanguage Deriving Church from L1-L3 Single Axioms Strategy in resolution-based theorem provers Intuitionistic Propositional Logic The positive implicational calculus Axiomatizing the CN fragment of intuitionistic logic Full intuitionistic logic Heyting’s theses Single Axioms Double Negation Elimination Double Negation Elimination The pushback lemmaMichael Beeson Logic and Computers The 200 kilobyte proof Many-Valued Propositional Logic Semantics of many-valued logic Lukasiewicz’s A1-A5 Dependence of A4 Distributive Laws Modal Logic Modal Logic Resolution-based metatheory Triviality in non-classical modal logics Conclusion Areas we don’t have time to discuss Open Problems and current research Summary Introduction Classical Propositional Logic Intuitionistic Propositional Logic Double Negation Elimination Many-Valued Propositional Logic Modal Logic Conclusion Early History In 1954, within a few years after computers were first up and running, Martin
    [Show full text]
  • Computer-Aided Studies of All Possible Shortest Single Axioms for the Equivalential Calculus
    COMPUTER-AIDED STUDIES OF ALL POSSIBLE SHORTEST SINGLE AXIOMS FOR THE EQUIVALENTIAL CALCULUS J.A. Kalman and J.G. Peterson Department of Mathematics and Statistics University of Auckland, New Zealand ABSTRACT produces the formula w if u and y are unifiable and w=o(v) for some most general unifier o of u and y; w is then unique to within variance (i.e. It has been known since 1939 that for a for• a formula w' may be produced by applying conden• mula to be a single axiom for the equivalential sed detachment to x and y if and only if w' is a calculus its length must be at least 11, and that variant of w), and it is customary to write single axioms of this length exist. Also, a single w»Dxy ; if x and y have variables in common, and axiom of length 11 must have the two-property. y' is a variant of y having no variables in common There are 630 formulas with the two-property and of with x, then Dxy is defined if and only if Dxy' is length 11. With computer assistance, the authors defined, and if Dxy' is defined we set Dxy«Dxy' . have shown that 612 of these 630 formulas are not Thus, if S is a deductive axiomatization of EC, single axioms. The main object of this paper is to and T is a set of equivalential tautologies such outline the methods used to obtain these results. that every formula in S is a substitution instance This paper logically precedes a recent paper of of a formula derivable by condensed detachment L.
    [Show full text]
  • Logical Basis for the Automation of Reasoning: Case Studies1
    Logical Basis for the Automation of Reasoning: Case Studies1 Larry Wos, Robert Veroff, and Gail W. Pieper Contents 1 Introduction . 1 2 The clause language paradigm . 3 2.1 Components of the clause language paradigm . 4 2.2 Interplay of the components . 6 3 A fragment of the history of automated reasoning 1960{2002 . 7 4 Answering open questions . 9 4.1 Robbins algebra . 10 4.2 Boolean algebra . 11 4.3 Logical calculi . 12 4.4 Combinatory logic . 14 4.5 Ortholattices . 15 5 Missing proofs and simpler proofs . 16 6 The clause language paradigm and other types of reasoning . 18 6.1 Logic programming . 19 6.2 Person-oriented reasoning . 21 7 Challenge problems for testing, comparing, and evaluating . 22 7.1 Combinatory logic . 22 7.2 Logical calculi . 23 7.3 Algebra . 24 8 Current state of the art . 25 9 Programs, books, and a database . 27 9.1 Reasoning programs for diverse applications . 27 9.2 Books for background and further research . 28 9.3 A database of test problems . 29 10 Summary and the future . 29 References . 31 1 Introduction With the availability of computers in the late 1950s, researchers began to entertain the possibility of automating reasoning. Immediately, two distinctly different approaches were considered as the possible basis for that automation. In one approach, the intention was to study and then emulate people; in the other, the plan was to rely on mathematical logic. 1This work was supported by the Mathematical, Information, and Computational Sciences Division subprogram of the Office of Advanced Scientific Computing Research, U.S.
    [Show full text]
  • Finding Missing Proofs with Automated Reasoning* Branden
    Finding Missing Proofs with Automated Reasoning* Branden Fitelson1,2 1University of Wisconsin Department of Philosophy Madison, WI 53706 Larry Wos2 2Mathematics and Computer Science Division Argonne National Laboratory Argonne, IL 60439-4801 Abstract This article features long-sought proofs with intriguing properties (such as the absence of double nega- tion and the avoidance of lemmas that appeared to be indispensable), and it features the automated methods for ®nding them. The theorems of concern are taken from various areas of logic that include two-valued sentential (or propositional) calculus and in®nite-valued sentential calculus. Many of the proofs (in effect) answer questions that had remained open for decades, questions focusing on axiomatic proofs. The approaches we take are of added interest in that all rely heavily on the use of a single pro- gram that offers logical reasoning, William McCune's automated reasoning program OTTER. The nature of the successes and approaches suggests that this program offers researchers a valuable automated assistant. This article has three main components. First, in view of the interdisciplinary nature of the audience, we discuss the means for using the program in question (OTTER), which ¯ags, parameters, and lists have which effects, and how the proofs it ®nds are easily read. Second, because of the variety of proofs that we have found and their signi®cance, we discuss them in a manner that permits comparison with the literature. Among those proofs, we offer a proof shorter than that given by Meredith and Prior in their treatment of Lukasiewicz's shortest single axiom for the implicational frag- ment of two-valued sentential calculus, and we offer a proof for the Lukasiewicz 23-letter single axiom for the full calculus.
    [Show full text]
  • On the Number of Unary-Binary Tree-Like Structures with Restrictions
    On the number of unary-binary tree-like structures with restrictions on the unary height Olivier Bodini,∗ Danièle Gardy,† Bernhard Gittenberger,‡ Zbigniew Gołębiewski,§ August 7, 2018 Abstract We consider various classes of Motzkin trees as well as lambda-terms for which we de- rive asymptotic enumeration results. These classes are defined through various restrictions concerning the unary nodes or abstractions, respectively: We either bound their number or the allowed levels of nesting. The enumeration is done by means of a generating function approach and singularity analysis. The generating functions are composed of nested square roots and exhibit unexpected phenomena in some of the cases. Furthermore, we present some observations obtained from generating such terms randomly and explain why usually powerful tools for random generation, such as Boltzmann samplers, face serious difficulties in generating lambda-terms. 1 Introduction This paper is mainly devoted to the asymptotic enumeration of lambda-terms belonging to a certain subclass of the class of all lambda-terms. Roughly speaking, a lambda-term is a formal expression built of variables and a quantifier λ which in general occurs more than once and acts on one of the free variables of the subsequent sub-term. Lambda calculus is a set of rules for manipulating lambda-terms and was invented by Church and Kleene in the 30ies (see [35, 36, 16]) in order to investigate decision problems. It plays an important rôle in computability theory, for automatic theorem proving or as a basis for some programming languages, e.g. LISP. Due to its flexibility it can be used for a formal description of programming in general and is therefore an essential tool for analyzing programming languages (cf.
    [Show full text]
  • A Finitely Axiomatized Formalization of Predicate Calculus with Equality
    A Finitely Axiomatized Formalization of Predicate Calculus with Equality Note: This is a preprint of Megill, \A Finitely Axiomatized Formalization of Predicate Calculus with Equality," Notre Dame Journal of Formal Logic, 36:435-453, 1995. The paper as published has the following errata that have been corrected in this preprint. • On p. 439, line 7, \(Condensed detachment)" should be followed by a reference to a footnote, \The arrays start at index i = 1. In Step 3, i is increased before each comparison is made." • On p. 446, line 17, \unnecessary" is misspelled. • On p. 448, 2nd line from bottom, \that in Section 8." should be followed by \In addition, S30 has the following stronger property." • On p. 449, line 22, \ui" should be \u1". • On p. 450, line 27, \Dpq" should be \Dqp". • On p. 451, line 2, \shorter proof string" should be followed by a reference to a footnote, \Found by the Otter theorem prover [20]." In August 2017, Tony H¨ager identified and provided the proofs for two miss- ing lemmas needed for the Substitution Theorem proof, and also found some shorter proofs for other lemmas. The necessary corrections have not yet been incorporated in this preprint but can be found in the discussion starting at https://groups.google.com/d/msg/metamath/t2G8X-dvTbA/Tqfxeo1sAwAJ A Finitely Axiomatized Formalization of Predicate Calculus with Equality July 7, 1995 Abstract We present a formalization of first-order predicate calculus with equality which, unlike traditional systems with axiom schemata or substitution rules, is finitely axiomatized in the sense that each step in a formal proof admits only finitely many choices.
    [Show full text]
  • Proof Finding Algorithms for Implicational Logics
    Theoretical Computer Science 232 (2000) 165{186 www.elsevier.com/locate/tcs View metadata, citation and similar papers at core.ac.uk brought to you by CORE Proof ÿnding algorithms for implicational logics provided by Elsevier - Publisher Connector M.W. Bunder Mathematics Department, University of Wollongong, Wollongong, NSW 2522, Australia Abstract The work in Bunder (Theoret. Comput. Sci. 169 (1996) 3{21) shows that for each one of many implicational logics the set of all lambda terms, that represent proofs in that logic, can be speciÿed. This paper gives, for most of these logics, algorithms which produce, for any given formula, a form of minimal proof within a ÿxed number of steps or otherwise a guarantee of unprovability. For the remaining logics there are similar algorithms that produce proofs, but not within a ÿxed number of steps. The new algorithms have been implemented in Oostdijk (Lambda Cal2). c 2000 Elsevier Science B.V. All rights reserved. Keywords: Proof ÿnding algorithms; Lambda calculus; Combinatory logic; Types; Substructural logics 1. Introduction An implicational logic can be speciÿed by the rule → ÿ → e ÿ and a set of axiom schemes. In this paper the axiom schemes we will be interested in will be taken from the following list: I → K → ÿ → B ( → ÿ) → ( → ) → → ÿ B0 ( → ÿ) → (ÿ → ) → → E-mail address: [email protected] (M.W. Bunder) 0304-3975/00/$ - see front matter c 2000 Elsevier Science B.V. All rights reserved. PII: S0304-3975(99)00174-7 166 M.W. Bunder / Theoretical Computer Science 232 (2000) 165{186 C ( → ÿ → ) → ÿ → → W ( → → ÿ) → → ÿ S ( → ÿ → ) → ( → ÿ) → → T → ( → ÿ → ) → ÿ → Logics will be named by their axiom schemes.
    [Show full text]
  • Missing Proofs Found
    Missing Pro ofs Found Branden Fitelson University of Wisconsin Department of Philosophy Madison WI and Mathematics and Computer Science Division Argonne National Lab oratory Argonne IL email telsonfacstawiscedu Larry Wos Mathematics and Computer Science Division Argonne National Lab oratory Argonne IL email wosmcsanlgov Abstract For close to a century despite the eorts of ne minds that include Hilb ert and Ackermann Lukasiewicz and Rose and Rosser various pro ofs of a number of signi cant theorems have remained missingat least not rep orted in the literatureamply demonstrating the depth of the corresp onding problems The types of such missing pro ofs are indeed diverse For one example a result may b e guaranteed provable b e cause of b eing valid and yet no pro of has b een found For a second example a theorem may have b een proved via metaargument but the desired axiomatic pro of based solely on the use of a given inference rule may have eluded the exp erts For a third example a theorem may have b een announced by a master but no pro of was supplied The nding of missing pro ofs of the cited types as well as of other types is the fo cus of this article The means to nding such pro ofs rests with heavy use of McCunes automated reasoning program OTTER reliance on a variety of p owerful strategies this program oers and employment of diverse metho dologies Here we present some of our successes and b ecause it may prove useful for circuit design and program synthesis as well as in the context of mathematics and logic detail our approach
    [Show full text]
  • From Automated Theorem Proving to Nuclear Structure Analysis with Self- Scheduled Task Parallelism
    Computational Nuclear Physics A Symposium in Honor of Steven C. Pieper 1 From Automated Theorem Proving to Nuclear Structure Analysis with Self- Scheduled Task Parallelism (a personal history of one programming model) Rusty Lusk (Ralph Butler) Mathematics and Computer Science Division Argonne National Laboratory Theme § Application programming models should be simple. § Their instantiations might be more complex, and their actual API’s might be even more so, not to mention their implementations. § Also, the programming models of the libraries that implement them might be more complex. § For example, the message passing model is simple: people are familiar with it from physical mail, phone calls, email, etc. § There have been several instantiations (PVM, Express, EUI, p4, etc.) and multiple implementations of MPI. – As an application programming model, MPI is simple because applications use the simple parts – the more exotic parts of MPI are used by libraries to implement simple application programming models (or should be). § MPI’s full API is a really a system programming model, driven by library developers developing portable libraries that implement simple programming models for applications. Example § Let’s discuss a simple programming model which has managed to remain simple through a number of instantiations and implementations. § It is related to, but not the same as, several current task-based systems. § It was how I wrote my first non-trivial parallel programs, back before the term “programming model” was in use (I didn’t know it was a programming model). § I call it “self-scheduled task parallelism” (SSTP). My first work in computer science, after a stab at (very) pure mathematics, was in automated theorem-proving, at Argonne with Larry Wos, Ross Overbeek, and Bill McCune.
    [Show full text]
  • Distributivity in Lℵ0 and Other Sentential Logics
    2 Harris & Fitelson Distributivity inL ℵ0 and Other Sentential Logics We choose Polish notation not just because of its historical dominance in this area, but also because of its syntactic economy. Some of the proofs we will present are quite complex and would be difficult to parse Kenneth Harris and Branden Fitelson and/or typeset in either the infix or the prefix notation used by Otter. University of Wisconsin–Madison The proofs presented in this paper have been translated directly 2 November 10, 2000 from Otter output files into our Polish notation. Hyperresolution is used, throughout, to implement all logical rules of inference in the Abstract. Certain distributivity results forLukasiewicz’s infinite-valued logicL ℵ0 are proved axiomatically (for the first time) with the help of the automated reasoning systems presented. The notation ‘[i, j, k]’written to the left of each program Otter [16]. In addition, non-distributivity results are established for a formula in our proofs is shorthand for ‘the present formula was obtained wide variety of positive substructural logics by the use of logical matrices discovered by applying the rule at line i (via a single hyperresolution step), with with the automated model findingprograms Mace [15] and MaGIC [25]. the formula at line j as major premise and the formula at line k as minor premise.’Rules of inference are stated using commas to separate the Keywords: distributivity, sentential, logic,Lukasiewicz, detachment, substructural premises of the rule, and a double arrow ‘⇒’to indicate its conclusion. For instance, modus ponens (or detachment) looks like: ‘Cpq,p ⇒ q’. 1.
    [Show full text]
  • 1 the Open Questions
    Answers to Some Open Questions of Ulrich & Meredith Matthew Walsh & Branden Fitelson† 06/26/21 1 The Open Questions Ulrich [11] poses twenty six open questions concerning the axiomatization of various sentential logics. In this note, we report solutions to three of these open questions involving axiomatizations of classical sentential logic. We adopt Ulrich’s notation (viz., traditional, Polish notation) throughout. And, the sole rule of inference we will be assuming throughout is condensed detachment [2]: from Cpq and p infer q (where C is the implication operator, and where most general substitution instances are used in each modus ponens inference). (Q1) Is Meredith’s [9] 21-symbol single axiom (M1) CCCCCpqCNrNsrtCCtpCsp for classical sentential logic the shortest possible (where N is the negation operator)? (Q2) Are Meredith’s [9] two 19-symbol single axioms (M4) CCCCCpqCrfstCCtpCrp (M5) CCCpqCCf r sCCspCtCup for classical sentential logic the shortest possible (where f is the constant falsum operator, which is equivalent to an arbitrary classical contradiction)? (Q3) Are Meredith’s [10] two 19-symbol single axioms (M2) CCCpqCrCosCCspCrCtp (M3) CCCpqCor CsCCr pCtCup for classical sentential logic the shortest possible (where o is the constant verum operator, which is equivalent to an arbitrary classical tautology)? In the next section, we report affirmative answers to each of these three questions, and we also report several new single axioms (of shortest length) for each of these three systems of classical sentential logic (thus answering three open questions posed by Meredith himself). Along the way, we will also pose several new open questions pertaining to these axiomatic systems.
    [Show full text]