Hausdorff dimension and oracle constructions

  • Authors:
  • John M. Hitchcock

  • Affiliations:
  • Department of Computer Science, University of Wyoming, WY

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2006

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Abstract

Bennett and Gill [Relative to a random oracle A, PA ≠ NPA ≠ co-NPA with probability 1, SIAM J. Comput. 10 (1981) 96-113] proved that PA ≠ NPA relative to a random oracle A, or in other words, that the set O[P=NP] = {A | PA = NPA} has Lebesgue measure 0. In contrast, we show that O[P=NP] has Hausdorff dimension 1.This follows from a much more general theorem: if there is a relativizable and paddable oracle construction for a complexity-theoretic statement Φ, then the set of oracles relative to which Φ holds has Hausdorff dimension 1.We give several other applications including proofs that the polynomial-time hierarchy is infinite relative to a Hausdorff dimension 1 set of oracles and that PA ≠ NPA ∩ coNPA relative to a Hausdorff dimension 1 set of oracles.