1、Using it the directed tree polynomial of a directed graph G can be found conveniently and efficiently.
2、如果此类材料能够普遍用于光学产业，这一突破带来的收益将是巨大的。
3、There are occasions when we want to refer to a directed tree, in which case it shall be said to be rooted at some vertex.
4、Its expansion gives all directed trees of the graph g.
