Computer Science Homework Solutions
Problem
#113569

Automata and Computability

Show the error in the following fallacious “proof” that P  NP.  Proof by contradiction.  Assume that P = NP.  Then SAT  P.  So, of some k, SAT  TIME(nk).  Because every language in NP is polynomial time reducible to SAT, NP  TIME(nk).  Therefore P  TIME(nk).  But, by the time hierarchy theorem, TIME(nk+1) contains a language which isn’t in TIME(nk), which contradicts P  TIME(nk).  Therefore P  NP.

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Problem A142.doc
Problem 42

Show the error in the following fallacious “proof” that P ( NP.
Proof by contradiction. Assume that P = NP. Then SAT ( P. So, of some
k, SAT ( TIME(nk). Because every language in NP is polynomial time
reducible to SAT, NP ( TIME(nk). Therefore P ( TIME(nk). But, by the
time hierarchy theorem, TIME(nk+1) contains a language which isn’t in
TIME(nk), which contradicts P ( TIME(nk). Therefore P ( NP.
Solution
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