November 8

November 8 - If A T B and B is decidable, then A is...

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Do not hand in your homework until the end of class November 8, 2005
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November 8, 2005 Agenda Last week Mapping reductions Turing reductions Today Review Tomorrow Begin computational complexity
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November 8, 2005 Announcement Homework due next Tuesday (11/15) 7.1 (a, b, e, f), 7.2 (a, b, e, f)
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November 8, 2005 Applications of mapping reductions • If A  m  B and B is decidable, then A is decidable • If A  m  B and A is undecidable, then B is  undecidable • If A  m  B and B is Turing-recognizable, then A is  Turing-recognizable  • If A  m  B and A is non-Turing-recognizable, then B  is non-Turing-recognizable
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November 8, 2005 Applications of Turing reductions
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Unformatted text preview: If A T B and B is decidable, then A is decidable If A T B and A is undecidable, then B is undecidable If A T B and B is Turing-recognizable, then A is Turing-recognizable If A T B and A is non-Turing-recognizable, then B is non-Turing-recognizable November 8, 2005 Today we will do examples Hint for problem 5.20 Show that L1 = {<M> | M is a TM and M halts on at least one input} is undecidable Is L2 = {<M,w,t> | M is a TM that accepts w in at least t steps} decidable? Prove your answer From Sipser 5.13, 5.14, 5.15, 5.24, 5.30 c...
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November 8 - If A T B and B is decidable, then A is...

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