The local search algorithm WSat is one of the most successful algorithms for solving the satisfiability (SAT) problem. It is notably effective at solving hard Random 3-SAT instances near the so-called `satisfiability threshold', but still shows a peak in search cost near the threshold and large variations in cost over different instances. We make a number of significant contributions to the analysis of WSat on high-cost random instances, using the recently-introduced concept of the backbone of a SAT instance. The backbone is the set of literals which are entailed by an instance. We find that the number of solutions predicts the cost well for small-backbone instances but is much less relevant for the large-backbone instances which appear near the threshold and dominate in the overconstrained region. We show a very strong correlation between search cost and the Hamming distance to the nearest solution early in WSat's search. This pattern leads us to introduce a measure of the backbone fragility of an instance, which indicates how persistent the backbone is as clauses are removed. We propose that high-cost random instances for local search are those with very large backbones which are also backbone-fragile. We suggest that the decay in cost beyond the satisfiability threshold is due to increasing backbone robustness (the opposite of backbone fragility). Our hypothesis makes three correct predictions. First, that the backbone robustness of an instance is negatively correlated with the local search cost when other factors are controlled for. Second, that backbone-minimal instances (which are 3-SAT instances altered so as to be more backbone-fragile) are unusually hard for WSat. Third, that the clauses most often unsatisfied during search are those whose deletion has the most effect on the backbone. In understanding the pathologies of local search methods, we hope to contribute to the development of new and better techniques.

Decision theory formally solves the problem of rational agents in uncertain worlds if the true environmental prior probability distribution is known. Solomonoff's theory of universal induction formally solves the problem of sequence prediction for unknown prior distribution. We combine both ideas and get a parameterless theory of universal Artificial Intelligence. We give strong arguments that the resulting AIXI model is the most intelligent unbiased agent possible. We outline for a number of problem classes, including sequence prediction, strategic games, function minimization, reinforcement and supervised learning, how the AIXI model can formally solve them. The major drawback of the AIXI model is that it is uncomputable. To overcome this problem, we construct a modified algorithm AIXI-tl, which is still effectively more intelligent than any other time t and space l bounded agent. The computation time of AIXI-tl is of the order tx2^l. Other discussed topics are formal definitions of intelligence order relations, the horizon problem and relations of the AIXI theory to other AI approaches.

Sony has provided a robot platform for research and development in physical agents, namely, fully autonomous legged robots. In this article, we describe our work using Sony's legged robots to participate at the RoboCup-98 legged robot demonstration and competition. Robotic soccer represents a challenging environment for research in systems with multiple robots that need to achieve concrete objectives, particularly in the presence of an adversary. Furthermore, RoboCup offers an excellent opportunity for robot entertainment. We introduce the RoboCup context and briefly present Sony's legged robot. We developed a vision-based navigation and a Bayesian localization algorithm. Team strategy is achieved through predefined behaviors and learning by instruction.

The information it provides a dynamic, real-time environment units resulting from such an analysis in which it is still relatively easy for tasks to be encode a deeper understanding of the timevarying classified, monitored, and assessed. Moreover, scene to be described. They include a commentary system has severe time restrictions spatial relations for the explicit characterization imposed by the flow of the game and is of spatial arrangements of objects as well thus a good test bed for research into real-time as representations of recognized object movements.

The Workshop on Intelligent Information Integration (III), organized in conjunction with the Sixteenth International Joint Conference on Artificial Intelligence, was held on 31 July 1999 in Stockholm, Sweden. Approximately 40 people participated, and nearly 20 papers were presented. This packed workshop schedule resulted from a large number of submissions that made it difficult to reserve discussion time without rejecting an unproportionately large number of papers. Participants included scientists and practitioners from industry and academia. Topics included query planning, applications of III, mediator architectures, and the use of ontologies for III.

Austin, Texas, the "live music capital For more information about AAAI is pleased to announce the continued Conferences/conferences.html. Expository Writing Award will be presented members. AAAI is delighted to announce the 31-August 3 in Austin, Texas. This The conference will be held July collocation of SARA-2000 with AAAIaward joins the two special awards 31-August 3, 2000, at the Austin Convention 2000. The Symposium on Abstraction, established last year, the AAAI Classic Center and Hyatt Regency Reformulation, and Approximation Paper Award and the AAAI Distinguished Austin in Austin, Texas. AAAI-2000 will be held July 26-29, just outside Austin in Lago Vista on Lake Travis, Service Award. For more information about The AAAI Effective Expository Writing the Innovative Applications of SARA-2000, please visit sara2000.unl. Award honors the author(s) of a Artificial Intelligence, the Mobile edu/ high-quality, effective piece of writing, Robot Competition and Exhibition, AAAI also welcomes SARA-2000 as accessible to the general public or the Intelligent Systems Demonstrations, our first affiliate conference. For more to a broad AI audience (not just a subarea), the Robot Building Laboratory, information about the AAAI Affiliates written within the last two and the Doctoral Consortium. New Program, please write to Carol Hamilton years. The contribution should be for 2000 will be a technical paper at hamilton@aaai.org. Nominated papers must be Uncertainty: Operations Research AAAI is pleased to announce the continuation in English and must have been published Meets AI (Again)"; Justine Cassell, of its Student Abstract and in a publicly accessible place "Why Do We Need a Body Anyway?"; Poster Program, the SIGART/AAAI (for example, periodical, hard copy, or Carla Gomes, "Structure, Duality, and Doctoral Consortium, and the AAAI online journal but not only as a web Randomization: Common Themes in Scholarship and Volunteer Programs. The author(s) AI and OR"; James Hendler, "Missed Students interested in attending the of the award-winning paper(s) will Perceptions: AI versus the Funding National Conference on Artificial receive a $2500 prize (shared if more Agencies"; Geoff Hinton, "Modeling Intelligence in Austin, July 31-August than one author) as well as lodging High-Dimensional Data Distributions 3, 2000, should consult the AAAI web and travel to the National Conference by Combining Simple Experts"; Rich site for further information about all on Artificial Intelligence.

They perform many different tasks, from giving tours to collecting trash. Many have distinguished themselves (usually with first-or second-place finishes) at various indoor and outdoor mobile robot competitions. Each case study is self-contained and includes detailed descriptions of important algorithms, including pseudo-code. Thus this volume serves as a recipe book for the design of successful mobile robot appli cations. Common themes include navigation and mapping, computer vision, and architecture.

By perceiving the with no adverse effects on the achievement world, each fully distributed agent builds a of G. Then, based can be thought of as times at which the on a complex set of behaviors, it chooses an team is "offline." In general (that is, when the agents are Although acting autonomously, each agent "online"), the domain is dynamic and real time, contributes to the overall team's goal. Agents receive sensory p at time t. The world state is directly accessible In the extreme, if q 0 or if x 0, then the to both internal and external behaviors.

Austin, Texas, the "live music capital For more information about AAAI is pleased to announce the continued Conferences/conferences.html. Expository Writing Award will be presented members. AAAI is delighted to announce the 31-August 3 in Austin, Texas. This The conference will be held July collocation of SARA-2000 with AAAIaward joins the two special awards 31-August 3, 2000, at the Austin Convention 2000. The Symposium on Abstraction, established last year, the AAAI Classic Center and Hyatt Regency Reformulation, and Approximation Paper Award and the AAAI Distinguished Austin in Austin, Texas. AAAI-2000 will be held July 26-29, just outside Austin in Lago Vista on Lake Travis, Service Award. For more information about The AAAI Effective Expository Writing the Innovative Applications of SARA-2000, please visit sara2000.unl. Award honors the author(s) of a Artificial Intelligence, the Mobile edu/ high-quality, effective piece of writing, Robot Competition and Exhibition, AAAI also welcomes SARA-2000 as accessible to the general public or the Intelligent Systems Demonstrations, our first affiliate conference. For more to a broad AI audience (not just a subarea), the Robot Building Laboratory, information about the AAAI Affiliates written within the last two and the Doctoral Consortium. New Program, please write to Carol Hamilton years. The contribution should be for 2000 will be a technical paper at hamilton@aaai.org. Nominated papers must be Uncertainty: Operations Research AAAI is pleased to announce the continuation in English and must have been published Meets AI (Again)"; Justine Cassell, of its Student Abstract and in a publicly accessible place "Why Do We Need a Body Anyway?"; Poster Program, the SIGART/AAAI (for example, periodical, hard copy, or Carla Gomes, "Structure, Duality, and Doctoral Consortium, and the AAAI online journal but not only as a web Randomization: Common Themes in Scholarship and Volunteer Programs. The author(s) AI and OR"; James Hendler, "Missed Students interested in attending the of the award-winning paper(s) will Perceptions: AI versus the Funding National Conference on Artificial receive a $2500 prize (shared if more Agencies"; Geoff Hinton, "Modeling Intelligence in Austin, July 31-August than one author) as well as lodging High-Dimensional Data Distributions 3, 2000, should consult the AAAI web and travel to the National Conference by Combining Simple Experts"; Rich site for further information about all on Artificial Intelligence.

The Bar Ilan Symposia on the Foundations of Artificial Intelligence are a series of research meetings held in Israel every two years. I report here on the sixth meeting, held in June 1999.