The Hedetniemi's conjecture was proposed in 1966. It stated that the chromatic number of the tensor product of two graph $G$ and $H$ is equal to the minimum of the individual chromatic numbers of the graphs $G$ and $H$. This conjecture was disproved by giving an explicit counterexample, by Yaroslav Shitov in 2019 in this paper published in Annals of Mathematics.
vidyarthi
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