König's lemma
This is an old revision of this page, as edited by Foxtrot (talk | contribs) at 21:47, February 23, 2008. It may differ significantly from current revision.
König's lemma (also spelled Koenig's lemma to avoid the trema) is a result in Zermelo-Fraenkel Set Theory and Graph Theory. It states that an infinite tree with finitely many branching degrees must have an infinite branch. Set theorists consider this to be an important transfinite generalization of the Pigeonhole Principle.