(2 +f(n))-SAT and its properties

  • Authors:
  • Yunlei Zhao;Xiaotie Deng;C. H. Lee;Hong Zhu

  • Affiliations:
  • Department of Computer Science, City University of Hong Kong, Hong Kong, China;Department of Computer Science, City University of Hong Kong, Hong Kong, China;Department of Computer Science, City University of Hong Kong, Hong Kong, China;Department of Computer Science, Fudan University, Shanghai, China

  • Venue:
  • Discrete Applied Mathematics - Discrete mathematics and theoretical computer science (DMTCS)
  • Year:
  • 2004

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Abstract

Consider a formula that contains n variables with the form Φ = Φ2 ∧ Φ3, where Φ2 is an instance of 2-SAT containing m2 2-clauses and Φ3 is an instance of 3-SAT containing m3 3-clauses. Φ is an instance of (2 + f(n))-SAT if m3/(m2 + m3) ≤ f(n). We prove that (2 + f(n))-SAT is in P if f(n) = O(log n/n2), and in NPC if f(n) = 1/n2-ε(∀ε: 0 n)k/n2)-SAT (k ≥ 2), for natural problems in NP - NPC - P (denoted as NPI) with respect to this (2 + f(n))-SAT model. We prove that the restricted version of it is not in NPC under P ≠ NP. Actually, it is indeed in NPI under some stronger but plausible assumption, specifically, the exponential-time hypothesis.