当所给风向图是欧拉图时，由这一近似算法求得的投递员路线是最优的投递员路线。
It is also shown that the postman route obtained by this approximation algorithm is optimal if the given windy graph is Eulerian.
若图G含有生成欧拉子图，则称G是超欧拉的。
A graph G is supereulerian if G has a spanning eulerian subgraph.
一个含有生成闭迹的图称为超欧拉图。
本文不利用收缩方法，直接证明了：当图G至多差一边有两棵边不相交的生成树时，G是超欧拉图或者G有割边。
In this note, no using the contraction method, we prove that if a graph G is one edge short of having two edge-disjoint spanning trees, then G has a cut edge or G is supereulerian.
主要考虑外平面图，系列平行图和平面欧拉图这三类特殊的平面图。
In this paper we prove that the problem is polynomial solvable on several special classes of graphs, such as outerplanar graphs, series-parallel graphs and Eulerian planar graphs.
主要考虑外平面图，系列平行图和平面欧拉图这三类特殊的平面图。
In this paper we prove that the problem is polynomial solvable on several special classes of graphs, such as outerplanar graphs, series-parallel graphs and Eulerian planar graphs.
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