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A reduction is the transformation of one problem into another problem. A example of using a reduction would be to be to show if a problem P is undecidable. This would be achieved by transforming or performing a reduction of a decision problem $P$ into an undecidable problem. If this can be achieved then we have shown that this problem P is undecidable.

5 votes
Accepted

Verifying that a reduction is correct

This is $\Pi_2^p$-complete. Let D be the usual reduction from SAT to CLIQUE. Let w be a string in CLIQUE. Consider a $\Pi_2^p$ language $L$ expressed as the set of $x$ such that for all $y$ there is a …
Lance Fortnow's user avatar
1 vote

Can a NEXP machine simulate invalid queries to a promise problem oracle?

Let's define what P$^A$ means in the promise setting: A language L is in P$^A$ if there is a polytime oracle machine $M$ such that for all sets $B$ such that $B$ contains $A_{YES}$ and $B\cap A_{NO}=\ …
Lance Fortnow's user avatar
34 votes
Accepted

Derandomizing Valiant-Vazirani?

Under the right derandomization assumptions (see Klivans-van Melkebeek) you get the following: There is a polytime computable $f(\phi)=(\psi_1,\ldots,\psi_k)$ s.t. for all $\phi$, If $\phi$ is satis …
Lance Fortnow's user avatar