关于树的另外一个性质 Theorem 4.9 Let T be a tree of order k.If G is a graph withδ（可≥k-1,then T is isomorphic to some subgraph of G.关于树的另外一个性质 Theorem 4.9 Let T be a tree of order k. If G is a graph with δ(G) ≥ k − 1, then T is isomorphic to some subgraph of G