Unformatted text preview: . “ . (where M , above, is a deterministic Turing machine) is NPcomplete. 5. A language L is co NPhard if for every L ∈ co NP it holds that L ≤ p L ; it is co NPcomplete if furthermore L ∈ co NP . Prove or disprove: L is NPcomplete iﬀ ¯ L is co NPcomplete. 6. Challenge question – optional. Show a universal nondeterministic Turing machine U such that (1) U ( M,x ) = M ( x ) for any nondeterministic Turing machine M for which M ( x ) is deﬁned, and (2) for every M there exists a constant c such that if M ( x ) runs in time T then U ( M,x ) runs in time O ( T ) (once again, the constant in the bigO notation may depend on M ). 1...
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 Fall '08
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 Nondeterministic Turing machine, Professor Jonathan Katz

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