The number of surjections between finite sets and the number of equivalent relations on finite sets are simply calculated by DUG three models.Two simple calculation formulas are given.A more gen-eral ball-box assignment problem is calculated by DUG three models.
关键词
满射个数/等价关系个数/DUG三模型/U数/G数
Key words
surjection/equivalent relation/DUG three models/U number/G number
维普
万方数据