8. Tree(*f)--A tree T of a connected graph G is a connected subgraph (子图) of G with the following properties: (a)T contains all the nodes of g; (b)T does not contain any loop The branches of g that are not tree branches are called links or chords(弦) The branches of a tree are called tree branches8. Tree（树）--A tree T of a connected graph G is a connected subgraph（子图） of G with the following properties: (a) T contains all the nodes of G; (b) T does not contain any loop. The branches of a tree are called tree branches. The branches of G that are not tree branches are called links or chords(弦）