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Linda Cook, Orientations of $P_4$ bind the dichromatic number
Linda Cook, Orientations of $P_4$ bind the dichromatic number
An oriented graph is a digraph that does not contain a directed cycle of length two. An (oriented) graph $D$ is $H$-free if $D$ does not contain $H$ as an induced sub(di)graph. The Gyárfás-Sumner conjecture is a widely-open conjecture on simple graphs, which states that for any forest $F$, there is some function $f$ such …