[Solved]: Has it been proven that the optimization TSP is (or is not) polynomial-time verifiable if P ≠ NP?

Problem Detail: The optimization version of TSP asks for the length of the shortest tour. Unlike the decision version of TSP, there’s no obvious way to verify a proposed solution of the optimization problem in polynomial time. But is there a proof of whether or not it can be verified in polynomial time assuming P ≠ NP?

Asked By : Mehrdad

Answered By : Scrub

If $optTSP$ is in $NP$, then $coNP = NP$. The latter is unresolved currently. Proof: if $optTSP$ is in $NP$, then $coTSP$ is in $coNP$ (the certificate being whatever certificate was provided to verify a solution to $optTSP$ was minimal, and then comparing the value of that solution to the desired bound). And because $TSP$ is $NP$-complete then this implies $NP = coNP$.
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