Postscript about NP-hard problems

  title={Postscript about NP-hard problems},
  author={Donald Ervin Knuth},
  journal={SIGACT News},
  • D. Knuth
  • Published 1 April 1974
  • Philosophy
  • SIGACT News
The proposal to call a problem NP-hard if every problem in NP reduces to it, as discussed in the January SIGACT newsletter, seems to have gotten widespread support. and no unfavorable reactions so far.) However, these people have convinced me that I should use reducibility in Cook's sense as opposed to Karp's in the definition of NP-hard. The main reason is that we naturally think of the complement of a problem being just as "hard" as that problem is, when using actual computers. This led me to… 
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