这个定理的直观含义是什么？ Theorem 8.4 A collection [SS2....S of nonempty finite sets has a system of distinct representatives if and only if for each integer k with 1 sks n,the union of any k of these sets contains at least k elements. For example,consider the sets SS2,.S,where Hal婚姻定理 S1={1,2,3}S2={2,4,6} S3={3,4,5} S4={1,4,7} S5={1,5,6}S6={3,6,7} S7={2,5,7} Then this collection of sets has a system of distinct representatives.In particular,1,2,..., 7(that is,iS for i=1,2,...,7)is a system of distinct representatives.On the other hand,the sets S1,2...where S1={1,3,5,6} S%={3,4} S3={4,5} S4={3,4,5} S5={1,2,4,6}S%={3,5}, do not have a system of distinct representatives asSS3,4,5 sodistinct representatives do not exist for the sets这个定理的直观含义是什么？ Hall 婚姻定理