Boolean formulas can be used to model real-world facts. In some situation we may havea Boolean formula that closely approximates a real-world fact, but we need to fine-tune itso that it models the real-world fact exactly. This is a problem of theory revision where thetheory is in the form of a Boolean formula. An algorithm is presented for revising a class ofBoolean formulas that are expressible as conjunctions of Horn clauses. Each of the clausesin the formulas considered here has a unique unnegated variable that does not appear inany other clauses, and is not `F'. The revision algorithm uses equivalence and membershipqueries to revise a given formula into a formula that is equivalent to an unknown targetformula having the same set of unnegated variables. The amount of time required by thealgorithm to perform this revision is logarithmic in the number of variables, and polynomialin the number of clauses in the unknown formula. An early version of this work waspresented at the 2003 Midwest Artificial Intelligence and Cognitive Science Conference [4].

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 106-117).

Thesis (Doctoral)--Technische Universiteit Eindhoven, 1996. / Contains summaries in English and Dutch. Vita. Includes bibliographical references (p. 145-154).

Η παρούσα διπλωµατική εργασία ασχολείται με το θέμα των Αλγορίθμων Επίλυσης Προβληµάτων SAT. Η εργασία αυτή εκπονήθηκε στα πλαίσια του Εργαστηρίου Ενσύρµατης Επικοινωνίας του Τµήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστηµίου Πατρών. Σκοπός της είναι η δημιουργία ενός Προσομοιωτή των αλγορίθμων αυτών, ο οποίος να μπορεί να προσπελαστεί από οποιονδήποτε μέσω του διαδικτύου. Αρχικά έγινε µία εισαγωγή στο αντικείμενο της Τεχνητής Νοημοσύνης και πιο συγκεκριµένα στην Προτασιακή Λογική, ενώ δόθηκε και το απαραίτητο υπόβαθρο για να κατανοηθεί το πρόβληµμα και οι τεχνικές λύσης του. Τέλος, επιλέχθηκε να γίνει η υλοποίηση του Προσωμοιωτή σε Java. / This diploma dissertation deals with SAT solvers, algorithms for the Boolean satisfiability problem. It was produced in the Wire Communications Laboratory of the Electrical and Computer Engineering Department of the University of Patras. Its aim is to create a simulator for these algorithms, accessible to anyone via the Internet. An introduction to the field of Artificial Intelligence and more specifically to Propositional Calculus was given as well as the necessary groundwork to understand the problem and its solution approaches. The simulation implementation was developed in Java

Apresentamos alguns aspectos da teoria de funções modais, que é o correlato modal da teoria de funções de verdade. Enquanto as fórmulas da lógica proposicional clássica expressam funções de verdade, as fórmulas da lógica proposicional modal (S5) expressam funções modais. Generalizamos alguns dos teoremas da teoria de funções de verdade para o caso modal; em particular, exibimos provas da completude funcional de alguns conjuntos de funções modais e definimos uma (nova) noção de reduto vero-funcional de funções modais, bem como a composição de funções modais em termos destes redutos. / We present some aspects of the theory of modal functions, which is the modal correlate of the theory of truth-functions. While the formulas of classical propositional logic express truth-functions, the formulas of modal propositional logic (S5) express modal functions. We generalize some theorems of the theory of truth-functions to the modal case; in particular, we show the functional completeness of some sets of modal functions and define a (new) notion of truth-functional reduct of modal functions, as well as the composition of modal functions in terms of such reducts.

La représentation des connaissances et les problèmes d’inférence associés restent à l’heure actuelle une problématique riche et centrale en informatique et plus précisément en intelligence artificielle. Dans ce cadre, la logique propositionnelle permet d’allier puissance d’expression et efficacité. Il reste que, tant que P est différent de NP, la déduction en logique propositionnelle ne peut admettre de solutions à la fois générales et efficaces. Dans cette thèse, nous adressons le problème de satisfiabilité et proposons de nouvelles classes d’instances pouvant être résolues de manière polynomiale.La découverte de nouvelles classes polynomiales pour SAT est à la fois importante d’un point de vue théorique et pratique. En effet, on peut espérer les exploiter efficacement au sein de solveurs SAT. Dans cette thèse, nous proposons d’étendre deux fragments polynomiaux de SAT à l’aide de la propagation unitaire tout en s’assurant que ces fragments demeurent reconnus et résolus de manière polynomiale. Le premier résultat de cette thèse concerne la classe Quad. Nous avons établi certaines propriétés de cette classe d’instances et avons étendu cette dernière de manière à s’abstraire de l’ordre imposé sur les littéraux. Le fragment obtenu en remplaçant cet ordre par différents ordres sur les clauses, conserve lamême complexité dans le pire cas. Nous avons également étudié l’impact de la résolution bornée et de la redondance par propagation unitaire sur cette classe. La seconde contribution concerne la classe polynomiale proposée par Tovey. La propagation unitaire est une nouvelle fois utilisée pour étendre cette classe. Nous comparons le nouveau fragment polynomial obtenu à deux autres classes basées également sur la propagation unitaire : Quad et UP-Horn. Nousapportons également une réponse à une question ouverte au sujet des connexions de ces classes. Nous montrons que UP-Horn et d’autres classes basées sur la propagation unitaire sont strictement incluses dans S Quad qui représente l’union de toutes les classes Quad obtenues par l’exploitation de tous les ordres sur les clauses possibles. / Knowledge representation and reasoning is a key issue in computer science and more particularly in artificial intelligence. In this respect, propositional logic is a representation formalism that is a good trade-off between the opposite computational efficiency and expressiveness criteria. However, unless P = NP, deduction in propositional logic is not polynomial in the worst case. So, in this thesis we propose new extensions of tractable classes of the propositional satisfiability problem. Tractable fragments of SAT play a role in the implementation of the most efficient current SAT solvers, many of thesetractable classes use the linear time unit propagation (UP) inference rule. We attempt to extend two of currently-known polynomial fragments of SAT thanks to UP in such a way that the fragments can still be recognized and solved in polynomial time. A first result focuses on Quad fragments: we establish some properties of Quad fragments and extend these fragments and exhibit promising variants. The extension is obtained by allowing Quad fixed total orderings of clauses to be accompanied with specific additional separate orderings of maximal sub-clauses. The resulting fragments extend Quad without degrading its worst-case complexity. Also, we investigate how bounded resolution and redundancy through unit propagation can play a role in this respect. The second contribution on tractable subclasses of SAT concerns extensions of one well-known Tovey’s polynomial fragment so that they also include instances that can be simplified using UP. Then, we compare two existing polynomial fragments based on UP: namely, Quad and UP-Horn. We also answer an open question about the connections between these two classes: we show that UP-Horn and some other UP-based variants are strict subclasses of S Quad, where S Quad is the union of all Quad classes obtained by investigating all possible orderings of clauses.

Military conflicts have become nonlinear and the interrelated political and socio-economic changes within these conflicts have created new challenges for American policymakers. A tool called Wallis' Propositional Analysis (PA) suggests a new paradigm that includes thinking about complexity and robustness/systemicity in a policy. The purpose of this single case study was to determine how the PA paradigm adds heuristic value to complex policy decision-making. A backdrop of Wallerstein's complexity theory and complex adaptive systems (CAS) guided this study. This study examined policy statements from the Obama administration on the Afghanistan and Pakistan conflicts in late December 2009. Data were coded and analyzed using Wallis' specific methodological approach that includes a systematic analysis of the policy's propositions and complexity and robustness/systemicity. Key findings indicated that the PA paradigm offers a heuristic method for how to think about the interrelated propositions within a policy that reflect the expected changes the policy intends to make. Specifically, this study demonstrated that an interwoven PA structural approach to policymaking affords the policymaker a method to consider the complex and nonlinear changes in the policy environment. By applying the PA paradigm, policymakers can positively impact social change by exploring policy options that consider a range of possible outcomes from the policy proposal, prior to policy implementation.

No description available.

No description available.

No description available.