at the same time, e call the number of oints of the largest lete grah subgrah included in figure f as “clique number“, and note it as x. it is easy to find that a lete grah of n oints requires at least n different colors because the to oints are adjacent.>
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it is obvious from the above that any art of a grah is divided and dyed to make any art ith mon sidelines have different colors, and can only use four colors, no more. the roosition is true.>