A logic for PTIME and a parameterized halting problem

  • Authors:
  • Yijia Chen;Jörg Flum

  • Affiliations:
  • Shanghai Jiaotong University, China;Albert-Ludwigs, Universität Freiburg, Germany

  • Venue:
  • Fields of logic and computation
  • Year:
  • 2010

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Abstract

In [9] Yuri Gurevich addresses the question whether there is a logic that captures polynomial time. He conjectures that there is no such logic. He considers a logic, we denote it by L≤, that allows to express precisely the polynomial time properties of structures; however, apparently, there is no algorithm "that given an L≤-sentence ϕ produces a polynomial time Turing machine that recognizes the class of models of ϕ." In [12] Nash, Remmel, and Vianu have raised the question whether one can prove that there is no such algorithm. They give a reformulation of this question in terms of a parameterized halting problem p-ACC≤ for nondeterministic Turing machines. We analyze the precise relationship between L≤ and p-ACC≤. Moreover, we show that p-ACC≤ is not fixed-parameter tractable if "P ≠ NP holds for all time constructible and increasing functions." A slightly stronger complexity theoretic hypothesis implies that L≤ does not capture polynomial time. Furthermore, we analyze the complexity of various variants of p-ACC≤ and address the construction problem associated with p-ACC≤.