Abstract
The upward separation technique was developed by Hartmanis, who used it to show thatE=NE iff there is no sparse set inNP -P [15]. This paper shows some inherent limitations of the technique. The main result of this paper is the construction of an oracle relative to which there are extremely sparse sets inNP-P, butNEE=EE; this is in contradiction to a result claimed in [14] and [16]. Thus, although the upward separation technique is useful in relating the existence of sets of polynomial (and greater) density inNP-P to the NTIME(T(n))=DTIME(T(n)) problem, the existence of sets ofvery low density inNP-P cannot be shown to have any bearing on this problem using proof techniques that relativize.
The oracle construction is also of interest since it is the first example of an oracle relative to whichEE=NEE andE ≠NE. (The techniques of [10], [17], [21], and [23] do not suffice to construct such an oracle.) The construction is novel and the techniques may be useful in other settings.
In addition, this paper also presents a number of new applications of the upward separation technique, including some new generalizations of the original result of [15].
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A preliminary version of this paper was presented at the 16th International Colloquium on Automata, Languages, and Programming [3]. The author was supported in part by National Science Foundation Research Initiation Grant Number CCR-8810467.
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Allender, E. Limitations of the upward separation technique. Math. Systems Theory 24, 53–67 (1991). https://doi.org/10.1007/BF02090390
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DOI: https://doi.org/10.1007/BF02090390