On finding extensions of default theories

  • Christos H. Papadimitriou
  • Martha Sideri
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 646)


We study from the computational standpoint the problem of finding an extension of a given default theory, and extend previous results in three directions. We show that all default theories that have no odd cycles (in some precise sense) have an extension, which can he found efficiently. We prove that it is NP-complete to find extensions even for default theories with no prerequisites and at most two literals per default. We also characterize precisely the complexity of finding extensions in general default theories: The problem is 2 P -complete.


Logic Program Conjunctive Normal Form Truth Assignment Extension Problem Default Theory 
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Copyright information

© Springer-Verlag Berlin Heidelberg 1992

Authors and Affiliations

  • Christos H. Papadimitriou
    • 1
  • Martha Sideri
    • 2
  1. 1.University of California at San DiegoUSA
  2. 2.Department of Computer ScienceAthens University of Economics and BusinessUSA

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