证明顶点数为n≥4,弧数为m≥(n-1/)+3的强连通定向图D中存在两点u^*、u^*,使得D—u^*和D-^*都是强连通的,并用例子说明这里所给的关于弧数的下界是紧的.
It is proved that a strongly connected oriented graph D with n ≥ 4 vertices and at least (n-1/2) + 3 arcs has two distinct vertices u*,v* such that both D - u* and D - v* are strongly connected. The examples show that the above lower bound on the number of arcs is sharp.