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Annals of Mathematics and Artificial Intelligence

, Volume 16, Issue 1, pp 183–236 | Cite as

Sorting, linear time and the satisfiability problem

  • Etienne Grandjean
Article

Abstract

Let DLIN denote the class of problems that are computable withinO(n/logn) uniform time on a RAM which can read its input (of lengthn) in blocks and which only uses integersO(n/logn). We prove that the sorting problem belongs to DLIN and formulate the Linear Time Thesis: “Each problem computable by a linear time bounded algorithm (in an intuitive sense) belongs to DLIN”. We also study the subclass DTIMESORT(n) of problems computable within linear time on a Turing machine using in addition a fixed number of sortings, and we show how the reductions of this class, so-called sort-lin reductions, are useful to classify NP problems: e.g. there is a sort-lin reduction from SAT to 3-SAT (using no sorting) and a sort-lin reduction from the NP-complete graph problem KERNEL to SAT (but we do not know of any similar reduction in DTIME(n)). Similarly, problem 2-SAT is linearly equivalent to the problem of Horn renaming (via sort-lin reductions). Finally, SAT is compared with many other combinatorial problems. A problemA is SAT-easy (resp. SAT-hard) if there is a sort-lin reduction fromA to SAT (resp. SAT toA). A SAT-equivalent problem is a problem both SAT-easy and SAT-hard. It is shown that the class of SAT-easy (resp. SAT-equivalent) problems is very large and that its generalization to so-called special clauses or, more generally, regular clauses, does not enlarge it. Moreover, we justify our opinion that problem SAT is, in some sense, a minimal NP-complete problem.

Keywords

Neural Network Sorting Linear Time Fixed Number Turing Machine 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© J.C. Baltzer AG, Science Publishers 1996

Authors and Affiliations

  • Etienne Grandjean
    • 1
  1. 1.GREYC, Université de CaenCaen CedexFrance

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