Higher complexity search problems for bounded arithmetic and a formalized no-gap theorem

  • Authors:
  • Neil Thapen

  • Affiliations:
  • Institute of Mathematics, Academy of Sciences of the Czech Republic, Praha 1, Czech Republic 115 67

  • Venue:
  • Archive for Mathematical Logic
  • Year:
  • 2011

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Abstract

We give a new characterization of the strict $$\forall {\Sigma^b_j}$$ sentences provable using $${\Sigma^b_k}$$ induction, for 1 驴 j 驴 k. As a small application we show that, in a certain sense, Buss's witnessing theorem for strict $${\Sigma^b_k}$$ formulas already holds over the relatively weak theory PV. We exhibit a combinatorial principle with the property that a lower bound for it in constant-depth Frege would imply that the narrow CNFs with short depth j Frege refutations form a strict hierarchy with j, and hence that the relativized bounded arithmetic hierarchy can be separated by a family of $$\forall {\Sigma^b_1}$$ sentences.