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评论
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对于n>0,也是覆盖{1..n}的拓扑数,其非空开集具有非空交集。还有覆盖{1..n}的拓扑数,其非空开集是成对相交的。例如,a(0)=1到a(3)=16拓扑(未显示空集)为:
{} {{1}} {{1,2}} {{1,2,3}}
{{1},{1,2}} {{1},{1,2,3}}
{{2},{1,2}} {{2},{1,2,3}}
{{3},{1,2,3}}
{{1,2},{1,2,3}}
{{1,3},{1,2,3}}
{{2,3},{1,2,3}}
{{1},{1,2},{1,2,3}}
{{1},{1,3},{1,2,3}}
{{2},{1,2},{1,2,3}}
{{2},{2,3},{1,2,3}}
{{3},{1,3},{1,2,3}}
{{3},{2,3},{1,2,3}}
{{1},{1,2},{1,3},{1,2,3}}
{{2},{1,2},{2,3},{1,2,3}}
{{3},{1,3},{2,3},{1,2,3}}
(结束)
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