Kruskal's tree theorem
In mathematics, Kruskal's tree theorem states that the set of finite trees over a wellquasiordered set of labels is itself wellquasiordered under homeomorphic embedding. The theorem was conjectured by Andrew Vázsonyi and proved by Joseph Kruskal (); a short proof was given by Crispin NashWilliams ().It has since become a prominent example in reverse mathematics as a statement that cannot ...
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