On a Problem in Graph Theory
On a Problem in Graph Theory
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关于图论中的一个问题
作者：
P. Erdös
假设有n个城镇，每对城镇都由一条单行道连接（道路只在城镇交汇）。是否有可能选择所有道路上的交通方向，以便如果任何两个城镇被命名，那么总是有第三个城镇可以通过道路直接到达这两个城镇？
Suppose there are n towns every pair of which are connected by a single one-way road (roads meet only at towns). Is it possible to choose the direction of the traffic on all the roads so that if any two towns are named there is always a third from which the two named can be reached directly by road?