Definition
Given two subsets A and B of N and a set of functions F from N to N which is closed under composition, A is called reducible to B under F if
We write
Let S be a subset of P(N) and ≤ a reduction, then S is called closed under ≤ if
A subset A of N is called hard for S if
A subset A of N is called complete for S if A is hard for S and A is in S.
Read more about this topic: Reduction (complexity)
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