Fig. 4

Correlation chain of retaining probability. Assume m _i  > m _j , node i is retained, if m _j is the only mark lower than m _i in C _i and j is not retained. The reason for j not being retained (j has the second lowest mark) is that k is retained, if m _k is the only mark lower than m_j in C _j . The solution is transformed to the retaining probability of node k