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7

An independent set that disconnects its graph is called an "independent cut", graphs that contain an independent cut are called "fragile graphs", and recognizing fragile graphs is known NP-complete [C. deFigueiredo, S. Klein, "NP-completeness of multipartite cutset testing", Congr. Numer. 119 (1996) 217–222, as cited by Guantao ...


6

First, I agree w/ Ludwik & other comments that I think (i) is unlikely. Polynomial-time reductions are just polynomial-time algorithms satisfying a certain (fairly flexible! compared to say p-time algorithms computing a fixed function $f$) input-output relationship, and polynomial-time algorithms are just too varied to say that they must take a certain ...


1

...aha, found it! This is the bipartite dimension problem, and yes it is NP-hard without further assumptions. Previously asked here: https://cs.stackexchange.com/questions/49266/finding-a-minimal-cover-of-a-subset-of-a-finite-cartesian-product-by-cartesian-p


5

I would imagine it very difficult to prove that "[a] certain type of gadget must exist for a reduction from 3-SAT to X". You could state that one type of gadget would enable a specific reduction, or even a family of reductions, but there might still be a different reduction possible that you haven't thought of. If you could indeed prove that every ...


6

If $G$ is $2k$-regular, then a relaxed edge coloring with exactly $k$ colors is the same thing as a 2-factorization, and is known to always exist by results of Petersen 1891. Otherwise, let $k=\lceil\Delta/2\rceil$ where $\Delta$ is the maximum degree of $G$. Then obviously, at least $k$ colors are needed in any relaxed coloring of $G$. But $G$ can be ...


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