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Polytime Manyone reduction: Clique to E-TM
• Last Updated : 30 Jun, 2020

Prerequisite – Clique is NP
A Polynomial-time reduction is a method for solving one problem using another.
E-TM = {<M> : M is a TM and }
CLIQUE = {<G, k> : graph G has a clique with at least k vertices}.

Note –
Since CLIQUE is NP => some NDTMCLIQUE accepts CLIQUE.

Reduction(<G, k>)
construct the following machine M
M(x):
1. Run NDTMCLIQUE on input <G, k>.
2. If NDTMCLIQUE accepts; M rejects x.
3. Else; M accepts x.
return <M>

We convert the instance <G, k> CLIQUE to a TM <M> E-TM. And <G, k> CLIQUE to a TM <M> E-TM.

Correctness:

i. <G, k>  CLIQUE => M rejects all input x => L(M)=  => <M>  E-TM.
ii. <G, k>  CLIQUE => M accepts all input x => L(M) => <M>  E-TM.

Hence, reduction is correct.

Polytime –
The reduction involves describing the construction of a new Turing machine M for input <G, k>. We don’t run the machine on the input. Hence, the reduction is polytime.

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