Session 1 -- Proofs About Lists Using Ellipsis -- Session 2 -- On the Complexity of Counting the Hilbert Basis of a Linear Diophantine System -- Solving Combinatorial Problems with Regular Local Search Algorithms -- Evidence Algorithm and Sequent Logical Inference Search -- Session 3 -- First Order Linear Temporal Logic over Finite Time Structures -- Model Checking Games for the Alternation-Free ?-Calculus and Alternating Automata -- Animating TLA Specifications -- Session 4 -- Transforming Conditional Rewrite Systems with Extra Variables into Unconditional Systems -- Cancellative Superposition Decides the Theory of Divisible Torsion-Free Abelian Groups -- Regular Sets of Descendants for Constructor-Based Rewrite Systems -- Session 5 -- Practical Reasoning for Expressive Description Logics -- Complexity of Terminological Reasoning Revisited -- Session 6 -- On the Complexity of Single-Rule Datalog Queries -- Session 7 -- Abstracting Properties in Concurrent Constraint Programming -- A Fixpoint Semantics for Reasoning about Finite Failure -- Extensions to the Estimation Calculus -- Session 8 -- Beth Definability for the Guarded Fragment -- Simplification of Horn Clauses That Are Clausal Forms of Guarded Formulas -- Session 9 -- Resource Management in Linear Logic Proof Search Revisited -- Focusing and Proof-Nets in Linear and Non-commutative Logic -- Session 10 -- CHAT Is ? (SLG-WAM) -- Proving Failure of Queries for Definite Logic Programs Using XSB-Prolog -- A Partial Evaluation Framework for Curry Programs.

This volume contains the papers presented at the Sixth International Conference on Logic for Programming and Automated Reasoning (LPAR'99), held in Tbilisi, Georgia, September 6-10, 1999, and hosted by the University of Tbilisi. Forty-four papers were submitted to LPAR'99. Each of the submissions was reviewed by three program committee members and an electronic program com­ mittee meeting was held via the Internet. Twenty-three papers were accepted. We would like to thank the many people who have made LPAR'99 possible. We are grateful to the following groups and individuals: to the program committee and the additional referees for reviewing the papers in a very short time, to the organizing committee, and to the local organizers of the INTAS workshop in Tbilisi in April 1994 (Khimuri Rukhaia, Konstantin Pkhakadze, and Gela Chankvetadze). And last but not least, we would like to thank Konstantin - rovin, who maintained the program committee Web page; Uwe Waldmann, who supplied macros for these proceedings and helped us to install some programs for the electronic management of the program committee work; and Bill McCune, who implemented these programs.