For the first problem, he goes to the trouble of defining "graph" and "tree", as though his audience has no math background, but doesn't bother defining "labele

For the first problem, he goes to the trouble of defining "graph" and "tree", as though his audience has no math background, but doesn't bother defining "labeled". For those wondering WTF an "unlabeled tree" is: http://mathworld.wolfram.com/LabeledGraph.html http://mathworld.wolfram.com/LabeledGraph.html