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Determining whether a propositional theory is satissable is a prototypical example of an NP-complete problem. Further, a large number of problems that occur in knowledge-representation, learning, planning, and other ares of AI are essentially sat-issability problems. This paper reports on the most extensive set of experiments to date on the location and(More)
Many reasoning and optimization problems exhibit symmetries. Previous work has shown how special purpose algorithms can make use of these symmetries to simplify reasoning. We present a general scheme whereby symmetries are exploited by adding \symmetry-breaking" predicates to the theory. Our approach can be used on any propo-sitional satissability problem,(More)
Determining whether a propositional theory is satissable is a prototypical example of an NP-complete problem. Further, a large number of problems that occur in knowledge representation, learning, planning, and other areas of AI are essentially satissability problems. This paper reports on a series of experiments to determine the location of the crossover(More)
Considerable progress has been made in recent years in understanding and solving propositional satisfia-bilit y problems. Much of this work has been based on experiments on randomly generated 3SAT problems . One generally accepted shortcoming of this work is that it is not clear how the results and algorithms developed will carry over to " real "(More)
The functional unit of an organ may be defined as the smallest, structurally distinct, ''self-sufficient'' unit that can independently subserve all known functions of that organ. The nephron is exemplary of such a concept, for it is both a well-defined functional and structural unit. A similar hepatic unit that can reconcile the dual vascular supply and the(More)
Qualitative reasoning can, and should, be decomposed into a model-building task, which creates a qualitative differential equation (QDE) as a model of a physical situation , and a qualitative simulation task, which starts with a QDE. and predicts the possible behaviors following from the model. In support of this claim, we present QPC, a model builder that(More)
Access-Limited Logic (ALL) is a theory of knowledge representation which formalizes the access limitations inherent in a network struc-tured knowledge-base. Where a deductive method such as resolution would retrieve all assertions that satisfy a given pattern, an access-limited logic retrieves only those assertions reachable by following an available access(More)
Small, extraportal, hepatic parenchymal cells, positive for biliary-type cytokeratins, may represent hepatic stem cells, canals of Hering (CoH), and/or ductal plate remnants. We evaluated these cells 3 dimensionally in normal human liver and massive necrosis. Tissues from normal human livers and from 1 liver with acetaminophen-induced massive necrosis were(More)
One of the fundamental problems in the theory of knowledge representation is the dii-culty of achieving both logical coherence and computational tractability. We present steps toward a theory of access-limited logic, in which access to assertions in the knowledge-base is constrained by semantic network style locality relations. Where a classical de-ductive(More)
OBJECTIVE To better understand the process by which pneumocytes can be derived from bone marrow cells, we investigated the in vivo kinetics of such engraftment following lethal irradiation. METHODS A cohort of lethally irradiated B6D2F1 female mice received whole bone marrow transplants (BMT) from age-matched male donors and were sacrificed at days 1, 3,(More)