设集合X={a1,a2,a3,…,an},f(n,m)表示X的含m个元素的不同封闭集族的数目。证明了f(n,m)={3n-2n,m=2;4n-2.3n+2n,m=3;5n-25.4n+2.3n-2n-1,m=4;6n-3.5n+3.4n-3n,m=5其中n=1,2,3,…。
Let X={a1,a2,a3,…,an}be a finite set and f(n,m)the number of closed family of sets with m elements of X.Then we show that: For every integer n≥1,f(n,m)={3n-2n,m=2;4n-2·3n+2n,m=3;5n-52·4n+2·3n-2n-1,m=4;6n-3·5n+3·4n-3n,m=5.