Nicholas Pippenger

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Extendible hashing is a new access technique, in which the user is guaranteed no more than two page faults to locate the data associated with a given unique identifier, or key. Unlike conventional hashing, extendible hashing has a dynamic structure that grows and shrinks gracefully as the database grows and shrinks. This approach simultaneously solves the(More)
Various computational models (such as machines and combinational logic networks) induce various and, m general, different computational complexity measures Relations among these measures are established by studying the ways m which one model can "simulate" another It ts shown that a machine with k-dimensional storage tapes (respectively, with(More)
We consider the problem of deciding whether a polygonal knot in 3-dimensional Euclidean space is unknotted, ie., capable of being continuously deformed without self-intersection so that it lies in a plane. We show that this problem, UNKNOTTING PROBLEM is in NP. We also consider the problem, SPLITTING PROBLEM of determining whether two or more such polygons(More)
It is shown that if formulas are used to compute Boolean functions in the presence of randomly occurring failures (as has been suggested by von Neumann and others), then 1) there is a limit shictly less than 1/2 to the failure probability per gate that can be tolerated, and 2) formulas that tolerate failures must be deeper (and, therefore, compute more(More)
We show that many Boolean functions (including, in a certain sense, "almost all" Boolean functions) have the property that the number of noisy gates needed to compute them differs from the number of noiseless gates by at most a constant factor. This may be contrasted with results of von Neumann, Dobrushin and Ortyukov to the effect that (1) for every(More)