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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)
Following a report of skeletal muscle regeneration from bone marrow cells, we investigated whether hepatocytes could also derive in vivo from bone marrow cells. A cohort of lethally irradiated B6D2F1 female mice received whole bone marrow transplants from age-matched male donors and were sacrificed at days 1, 3, 5, and 7 and months 2, 4, and 6(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)
Many classes of reasoning problems display a large amount of symmetry. In mathematical and common-sense reasoning, such symmetries are often used to reduce the diiculty of reasoning. In this paper we show how symmetries can be used in automated reasoning both to reduce or avoid case analysis, and to reduce the scope of existential quantiication. We show(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)