Hard instances of algorithms and proof systems

  • Authors:
  • Yijia Chen;Jörg Flum;Moritz Müller

  • Affiliations:
  • Department of Computer Science and Engineering, Shanghai Jiao Tong University, Shanghai, China;Abteilung für mathematische Logik, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany;Kurt Gödel Research Center for Mathematical Logic, Wien, Austria

  • Venue:
  • CiE'12 Proceedings of the 8th Turing Centenary conference on Computability in Europe: how the world computes
  • Year:
  • 2012

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Abstract

If the class Taut of tautologies of propositional logic has no almost optimal algorithm, then every algorithm $\mathbb{A}$ deciding Taut has a polynomial time computable sequence witnessing that $\mathbb{A}$ is not almost optimal. We show that this result extends to every $\Pi_t^p$-complete problem with t≥1; however, assuming the Measure Hypothesis, there is a problem which has no almost optimal algorithm but is decided by an algorithm without such a hard sequence. Assuming that a problem Q has an almost optimal algorithm, we analyze whether every algorithm deciding Q, which is not almost optimal algorithm, has a hard sequence.