PHIL12A Section Answers, 14 February 2011
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Logic: Representation and Automated Reasoning
Logic Knowledge Representation & Reasoning Mechanisms Logic ● Logic as KR ■ Propositional Logic ■ Predicate Logic (predicate Calculus) ● Automated Reasoning ■ Logical inferences ■ Resolution and Theorem-proving Logic ● Logic as KR ■ Propositional Logic ■ Predicate Logic (predicate Calculus) ● Automated Reasoning ■ Logical inferences ■ Resolution and Theorem-proving Propositional Logic ● Symbols: ■ truth symbols: true, false ■ propositions: a statement that is “true” or “false” but not both E.g., P = “Two plus two equals four” Q = “It rained yesterday.” ■ connectives: ~, →, ∧, ∨, ≡ • Sentences - propositions or truth symbols • Well formed formulas (expressions) - sentences that are legally well-formed with connectives E.g., P ∧ R → and P ~ are not wff but P ∧ R → ~ Q is Examples P Q AI is hard but it is interesting P ∧ Q AI is neither hard nor interesting ~P ∧ ~ Q P Q If you don’t do assignments then you will fail P → Q ≡ Do assignments or fail (Prove by truth table) ~ P ∨ Q None or both of P and Q is true (~ P ∧ ~ Q) ∨ (P ∧ Q) ≡ T Exactly one of P and Q is true (~ P ∧ Q) ∨ (P ∧ ~ Q) ≡ T Predicate Logic ● Symbols: • truth symbols • constants: represents objects in the world • variables: represents ranging objects } Terms • functions: represent properties • Predicates: functions of terms with true/false values e.g., bill_residence_city (vancouver) or lives (bill, vancouver) ● Atomic sentences: true, false, or predicates ● Quantifiers: ∀, ∃ ● Sentences (expressions): sequences of legal applications of connectives and quantifiers to atomic -
Boolean Satisfiability Solvers: Techniques and Extensions
Boolean Satisfiability Solvers: Techniques and Extensions Georg WEISSENBACHER a and Sharad MALIK a a Princeton University Abstract. Contemporary satisfiability solvers are the corner-stone of many suc- cessful applications in domains such as automated verification and artificial intelli- gence. The impressive advances of SAT solvers, achieved by clever engineering and sophisticated algorithms, enable us to tackle Boolean Satisfiability (SAT) problem instances with millions of variables – which was previously conceived as a hope- less problem. We provide an introduction to contemporary SAT-solving algorithms, covering the fundamental techniques that made this revolution possible. Further, we present a number of extensions of the SAT problem, such as the enumeration of all satisfying assignments (ALL-SAT) and determining the maximum number of clauses that can be satisfied by an assignment (MAX-SAT). We demonstrate how SAT solvers can be leveraged to solve these problems. We conclude the chapter with an overview of applications of SAT solvers and their extensions in automated verification. Keywords. Satisfiability solving, Propositional logic, Automated decision procedures 1. Introduction Boolean Satisfibility (SAT) is the problem of checking if a propositional logic formula can ever evaluate to true. This problem has long enjoyed a special status in computer science. On the theoretical side, it was the first problem to be classified as being NP- complete. NP-complete problems are notorious for being hard to solve; in particular, in the worst case, the computation time of any known solution for a problem in this class increases exponentially with the size of the problem instance. On the practical side, SAT manifests itself in several important application domains such as the design and verification of hardware and software systems, as well as applications in artificial intelligence. -
Deduction (I) Tautologies, Contradictions And
D (I) T, & L L October , Tautologies, contradictions and contingencies Consider the truth table of the following formula: p (p ∨ p) () If you look at the final column, you will notice that the truth value of the whole formula depends on the way a truth value is assigned to p: the whole formula is true if p is true and false if p is false. Contrast the truth table of (p ∨ p) in () with the truth table of (p ∨ ¬p) below: p ¬p (p ∨ ¬p) () If you look at the final column, you will notice that the truth value of the whole formula does not depend on the way a truth value is assigned to p. The formula is always true because of the meaning of the connectives. Finally, consider the truth table table of (p ∧ ¬p): p ¬p (p ∧ ¬p) () This time the formula is always false no matter what truth value p has. Tautology A statement is called a tautology if the final column in its truth table contains only ’s. Contradiction A statement is called a contradiction if the final column in its truth table contains only ’s. Contingency A statement is called a contingency or contingent if the final column in its truth table contains both ’s and ’s. Let’s consider some examples from the book. Can you figure out which of the following sentences are tautologies, which are contradictions and which contingencies? Hint: the answer is the same for all the formulas with a single row. () a. (p ∨ ¬p), (p → p), (p → (q → p)), ¬(p ∧ ¬p) b. -
First-Order Logic
First-Order Logic Chapter 8 1 Outline • Why FOL? • Syntax and semantics of FOL • Using FOL • Wumpus world in FOL • Knowledge engineering in FOL 2 Pros and cons of propositional logic ☺ Propositional logic is declarative ☺ Propositional logic allows partial/disjunctive/negated information – (unlike most data structures and databases) ☺ Propositional logic is compositional: – meaning of B1,1 ∧ P1,2 is derived from meaning of B1,1 and of P1,2 ☺ Meaning in propositional logic is context-independent – (unlike natural language, where meaning depends on context) Propositional logic has very limited expressive power – (unlike natural language) – E.g., cannot say "pits cause breezes in adjacent squares“ • except by writing one sentence for each square 3 First-order logic • Whereas propositional logic assumes the world contains facts, • first-order logic (like natural language) assumes the world contains – Objects: people, houses, numbers, colors, baseball games, wars, … – Relations: red, round, prime, brother of, bigger than, part of, comes between, … – Functions: father of, best friend, one more than, plus, … 4 Syntax of FOL: Basic elements • Constants KingJohn, 2, NUS,... • Predicates Brother, >,... • Functions Sqrt, LeftLegOf,... • Variables x, y, a, b,... • Connectives ¬, ⇒, ∧, ∨, ⇔ • Equality = • Quantifiers ∀, ∃ 5 Atomic sentences Atomic sentence = predicate (term1 ,...,termn) or term = term 1 2 Term = function (term1,..., termn) or constant or variable • E.g., Brother(KingJohn,RichardTheLionheart) > (Length(LeftLegOf(Richard)), Length(LeftLegOf(KingJohn))) -
Solving the Boolean Satisfiability Problem Using the Parallel Paradigm Jury Composition
Philosophæ doctor thesis Hoessen Benoît Solving the Boolean Satisfiability problem using the parallel paradigm Jury composition: PhD director Audemard Gilles Professor at Universit´ed'Artois PhD co-director Jabbour Sa¨ıd Assistant Professor at Universit´ed'Artois PhD co-director Piette C´edric Assistant Professor at Universit´ed'Artois Examiner Simon Laurent Professor at University of Bordeaux Examiner Dequen Gilles Professor at University of Picardie Jules Vernes Katsirelos George Charg´ede recherche at Institut national de la recherche agronomique, Toulouse Abstract This thesis presents different technique to solve the Boolean satisfiability problem using parallel and distributed architec- tures. In order to provide a complete explanation, a careful presentation of the CDCL algorithm is made, followed by the state of the art in this domain. Once presented, two proposi- tions are made. The first one is an improvement on a portfo- lio algorithm, allowing to exchange more data without loosing efficiency. The second is a complete library with its API al- lowing to easily create distributed SAT solver. Keywords: SAT, parallelism, distributed, solver, logic R´esum´e Cette th`ese pr´esente diff´erentes techniques permettant de r´esoudre le probl`eme de satisfaction de formule bool´eenes utilisant le parall´elismeet du calcul distribu´e. Dans le but de fournir une explication la plus compl`ete possible, une pr´esentation d´etaill´ee de l'algorithme CDCL est effectu´ee, suivi d'un ´etatde l'art. De ce point de d´epart,deux pistes sont explor´ees. La premi`ereest une am´eliorationd'un algorithme de type portfolio, permettant d'´echanger plus d'informations sans perte d’efficacit´e. -
Atomic Sentences
Symbolic Logic Study Guide: Class Notes 5 1.2. Notes for Chapter 2: Atomic Sentences 1.2.1. The Basic Structure of Atomic Sentences (2.1, 2.2, 2.3, and 2.5 of the Text) 1. Comparison between simple English sentences and atomic sentences Simple English Sentences Atomic sentences (FOL) (subject-predicate sentences) John is a freshman Freshman (John) John swims. Swim (John) John loves Jenny. Love (John, Jenny) John prefers Jenny to Amy. Prefer (John, Jenny, Amy) John’s mother loves Jenny. Love (mother (John), Jenny) The father of Jenny is angry. Angry (father (Jenny)) John is the brother of Jenny. John = brother (Jenny) [relational identity] 2. Names Definition: Names are individual constants that refer to some fixed individual objects or other. (1) The rule of naming (p. 10) • No empty name. • No multiple references (do not use one name to refer to different objects). • Multiple names: you can name one object by different names. (2) General terms / names: using a predicate, instead of a constant, to represent a general term. For example, John is a student Student (John) [correct] John = student [wrong!!!] 3. Predicates Definition: Predicates are symbols used to denote some property of objects or some relationship between objects. (1) Arity of predicates • Unary predicates--property • Binary predicates Relations • Ternary predicates (2) The predicates used in Tarski’s World: see p. 11. (3) Two rules of predicates: see p.12. 6 Symbolic Logic Study Guide: Class Notes 4. Functions Definition: A function is an individual constant determined by another constant. (1) Comparison with names: • Both refer to some fixed individual objects. -
1 Winnowing Wittgenstein: What's Worth Salvaging from the Wreck Of
Winnowing Wittgenstein: What’s Worth Salvaging from the Wreck of the Tractatus Peter Simons Trinity College Dublin Abstract Wittgenstein’s Tractatus still harbours valuable lessons for contemporary philosophy, but which ones? Wittgenstein’s long list of things we cannot speak about is set aside, but his insistence that the logical constants do not represent is retained, as is the absolute distinction between names and sentences. We preserve his atomism of elementary sentences but discard the atomism of simple objects in states of affairs. The fundamental harmony between language and the world is rejected: it is the source of much that is wrong in the Tractatus. What remains is a clarified role for items in making elementary sentences true. 1 Introduction Kevin Mulligan has maintained throughout his philosophical career a keen and judicious appreciation of the chief figures of that great philosophical explosion centred on Austria in the 19th and early 20th century. Of these figures, the best-known and most widely influential is Ludwig Wittgenstein.1 Kevin has maintained, quite rightly, that it is impossible to appreciate the extent to which Wittgenstein’s contributions to philosophy are as original as his many admirers contend without a great deal more knowledge of the Central European milieu from which Wittgenstein emerged than the majority of these admirers care to or are prepared to investigate. In this respect the more diffuse and ample later philosophy presents a much greater challenge than the early work which culminated in the Logisch-philosophische Abhandlung.2 The modest extent of the Tractatus and its more limited period of genesis, as well as its relatively crisper form and content, render it a more manageable and ultimately less controversial work than the post-Tractarian writings, whose thrust is even today occasionally obscure, despite more than a half century of frenzied exegesis. -
12 Propositional Logic
CHAPTER 12 ✦ ✦ ✦ ✦ Propositional Logic In this chapter, we introduce propositional logic, an algebra whose original purpose, dating back to Aristotle, was to model reasoning. In more recent times, this algebra, like many algebras, has proved useful as a design tool. For example, Chapter 13 shows how propositional logic can be used in computer circuit design. A third use of logic is as a data model for programming languages and systems, such as the language Prolog. Many systems for reasoning by computer, including theorem provers, program verifiers, and applications in the field of artificial intelligence, have been implemented in logic-based programming languages. These languages generally use “predicate logic,” a more powerful form of logic that extends the capabilities of propositional logic. We shall meet predicate logic in Chapter 14. ✦ ✦ ✦ ✦ 12.1 What This Chapter Is About Section 12.2 gives an intuitive explanation of what propositional logic is, and why it is useful. The next section, 12,3, introduces an algebra for logical expressions with Boolean-valued operands and with logical operators such as AND, OR, and NOT that Boolean algebra operate on Boolean (true/false) values. This algebra is often called Boolean algebra after George Boole, the logician who first framed logic as an algebra. We then learn the following ideas. ✦ Truth tables are a useful way to represent the meaning of an expression in logic (Section 12.4). ✦ We can convert a truth table to a logical expression for the same logical function (Section 12.5). ✦ The Karnaugh map is a useful tabular technique for simplifying logical expres- sions (Section 12.6). -
Chapter 1. Sentential Logic
CHAPTER 1. SENTENTIAL LOGIC 1. Introduction In sentential logic we study how given sentences may be combined to form more complicated compound sentences. For example, from the sentences 7 is prime, 7 is odd, 2 is prime, 2 is odd, we can obtain the following sentences: • 7 is prime and 7 is odd • 7 is odd and 2 is odd • 7 is odd or 2 is odd • 7 is not odd • If 2 is odd then 2 is prime Of course, this process can be iterated as often as we want, obtaining also: • If 7 is not odd then 2 is odd • If 7 is odd and 2 is odd then 2 is not prime • (7 is odd and 2 is odd) or 2 is prime We have improved on English in the last example by using parentheses to resolve an ambiguity. And, or, not, if . then (or implies) are called (sentential) connectives. Using them we can define more connectives, for example 2 is prime iff 2 is odd can be defined as (If 2 is prime then 2 is odd) and (if 2 is odd then 2 is prime). The truth value of any compound sentence is determined completely by the truth values of its component parts. For example, assuming 2, 7, odd, prime all have their usual meanings then 7 is odd and 2 is odd is false but (7 is odd and 2 is odd) or 2 is prime is true. We will discuss implication later. In the formal system of sentential logic we study in this Chapter, we do not use English sentences, but build the compound sentences from an infinite collection of symbols which we think of as referring to sentences — since these are not built up from other sentences we refer to them as atomic sentences. -
Logic, Proofs
CHAPTER 1 Logic, Proofs 1.1. Propositions A proposition is a declarative sentence that is either true or false (but not both). For instance, the following are propositions: “Paris is in France” (true), “London is in Denmark” (false), “2 < 4” (true), “4 = 7 (false)”. However the following are not propositions: “what is your name?” (this is a question), “do your homework” (this is a command), “this sentence is false” (neither true nor false), “x is an even number” (it depends on what x represents), “Socrates” (it is not even a sentence). The truth or falsehood of a proposition is called its truth value. 1.1.1. Connectives, Truth Tables. Connectives are used for making compound propositions. The main ones are the following (p and q represent given propositions): Name Represented Meaning Negation p “not p” Conjunction p¬ q “p and q” Disjunction p ∧ q “p or q (or both)” Exclusive Or p ∨ q “either p or q, but not both” Implication p ⊕ q “if p then q” Biconditional p → q “p if and only if q” ↔ The truth value of a compound proposition depends only on the value of its components. Writing F for “false” and T for “true”, we can summarize the meaning of the connectives in the following way: 6 1.1. PROPOSITIONS 7 p q p p q p q p q p q p q T T ¬F T∧ T∨ ⊕F →T ↔T T F F F T T F F F T T F T T T F F F T F F F T T Note that represents a non-exclusive or, i.e., p q is true when any of p, q is true∨ and also when both are true. -
Logic, Sets, and Proofs David A
Logic, Sets, and Proofs David A. Cox and Catherine C. McGeoch Amherst College 1 Logic Logical Statements. A logical statement is a mathematical statement that is either true or false. Here we denote logical statements with capital letters A; B. Logical statements be combined to form new logical statements as follows: Name Notation Conjunction A and B Disjunction A or B Negation not A :A Implication A implies B if A, then B A ) B Equivalence A if and only if B A , B Here are some examples of conjunction, disjunction and negation: x > 1 and x < 3: This is true when x is in the open interval (1; 3). x > 1 or x < 3: This is true for all real numbers x. :(x > 1): This is the same as x ≤ 1. Here are two logical statements that are true: x > 4 ) x > 2. x2 = 1 , (x = 1 or x = −1). Note that \x = 1 or x = −1" is usually written x = ±1. Converses, Contrapositives, and Tautologies. We begin with converses and contrapositives: • The converse of \A implies B" is \B implies A". • The contrapositive of \A implies B" is \:B implies :A" Thus the statement \x > 4 ) x > 2" has: • Converse: x > 2 ) x > 4. • Contrapositive: x ≤ 2 ) x ≤ 4. 1 Some logical statements are guaranteed to always be true. These are tautologies. Here are two tautologies that involve converses and contrapositives: • (A if and only if B) , ((A implies B) and (B implies A)). In other words, A and B are equivalent exactly when both A ) B and its converse are true. -
Introduction to the Boolean Satisfiability Problem
Introduction to the Boolean Satisfiability Problem Spring 2018 CSCE 235H Introduction to Discrete Structures URL: cse.unl.edu/~cse235h All questions: Piazza Satisfiability Study • 7 weeks • 30 min lectures in recitation • ~2 hours of homework per week • Goals: – Exposure to fundamental research in CS – Understand how to model problems – Learn to use SAT solver, MiniSAT CSCE 235 Logic 2 Boolean Satisfiability Problem • Given: – A Boolean formula • Question: – Is there an assignment of truth values to the Boolean variables such that the formula holds true? CSCE 235 Logic 3 Boolean Satisfiability Problem a ( a b) _ ¬ ^ (a a) (b b) _ ¬ ! ^ ¬ CSCE 235 Logic 4 Boolean Satisfiability Problem a ( a b) _ ¬ ^ SATISFIABLE a=true, b=true (a a) (b b) _ ¬ ! ^ ¬ CSCE 235 Logic 5 Boolean Satisfiability Problem a ( a b) _ ¬ ^ SATISFIABLE a=true, b=true (a a) (b b) _ ¬ ! ^ ¬ UNSATISFIABLE Left side of implication is a tautology. Right side of implication is a contradiction. True cannot imply false. CSCE 235 Logic 6 Applications of SAT • Scheduling • Resource allocation • Hardware/software verification • Planning • Cryptography CSCE 235 Logic 7 Conjunctive Normal Form • Variable a, b, p, q, x1,x2 • Literal a, a, q, q, x , x ¬ ¬ 1 ¬ 1 • Clause (a b c) _ ¬ _ • Formula (a b c) _ ¬ _ (b c) ^ _ ( a c) ^ ¬ _ ¬ CSCE 235 Logic 8 Converting to CNF • All Boolean formulas can be converted to CNF • The operators can be rewritten in , , terms of ! $,⊕, ¬ _ ^ • , , can be rearranged using ¬– De Morgan_ ^ ’s Laws – Distributive Laws – Double Negative • May result in exponential