Talk:Handshaking lemma

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I read: "every finite undirected graph has an even number of vertices with odd degree"

Why is the graph supposed undirected?

It seems to me this this lemma is also valid for directed graphs...

For directed graphs there may exit odd numbers of vertices with odd indegree or odd outdegree (consider the graph with one directed edge). It's true for total degree but that's essentially the same as the degree in the underlying undirected graph. —David Eppstein (talk) 15:52, 28 September 2013 (UTC)