Some 3CNF properties are hard to test

  • Authors:
  • Eli Ben-Sasson;Prahladh Harsha;Sofya Raskhodnikova

  • Affiliations:
  • Harvard & MIT, Cambridge, MA;Massachusetts Institute of Technology, Cambridge, MA;Massachusetts Institute of Technology, Cambridge, MA

  • Venue:
  • Proceedings of the thirty-fifth annual ACM symposium on Theory of computing
  • Year:
  • 2003

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Abstract

For a boolean formula φ on n variables, the associated property Pφ is the collection of n-bit strings that satisfy φ. We prove that there are 3CNF properties that require a linear number of queries, even for adaptive tests. This contrasts with 2CNF properties that are testable with O(√n) queries[7]. Notice that for every bad instance (i.e. an assignment that does not satisfy φ) there is a 3-bit query that witnesses this fact. Nevertheless, finding such a short witness requires a linear number of queries, even for assignments that are very far from satisfying.We provide sufficient conditions for linear properties to be hard to test, and in the course of the proof include a couple of observations which are of independent interest.