For regular simple Backward Search Alg-orithm (Algorithm SB), Cs, the expected branch number of the vertices on its Backward Search Tree, is equal to the average of the average outdegree of the useful vertices on the present graph of each level.

• 对于常规的简单 回溯法SB，回溯树上各顶点的期望分枝数cs等于各层当前可用顶点的平均出度的 平均值。