David A. Wolfram

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Gray [14] identifies the origins of sheaf theory in algebraic topology in the works of Alexander [1] in 1938, and Leray [15] in 1945. Apart from algebraic topology, Gray also describes its grasp on complex analysis, algebraic geometry, differential equations, and category theory. Sheaves have more recently been used as models for concurrency. Perhaps the(More)
Restrictions of the problem of finding all maximal unifiable or minimal nonunifiable subsets to those of certain sizes are shown to be NP-hard, and consequently inappropriate in general for reducing thrashing by intelligent backtracking in resolution theorem provers and logic program executions. We also show that existing backtrack methods based on the(More)
INTERNIST-I was an expert system designed in the early 1970's to diagnose multiple diseases in internal medicine by modelling the behaviour of clinicians. Its form and operation are described, and evaluations of the system are surveyed. The major result of the project was its knowledge base which has been used in successor systems for medical education and(More)
Forward checking (FC) [l] is similar to backtracking except that after a choice is made, the sets containing possible future choices are pushed on a stack and filtered [5] by deleting inconsistent choices from them. If ever a selected set is empty, the stack is popped to find a previously selected set which is not empty. FC has principally been used to(More)
Kimba is the rst model generation program which implements a semi-decision procedure for nite satissability of rst-order logics with nitely many truth values. The procedure enumerates the nite models of its input and can be used to compute eeciently domain minimal models whose positive part is minimal in size. Kimba has been implemented in the constraint(More)