R.P.Stanley,《枚举组合数学》,剑桥,第1卷,第3章,第98页,图3-1(或第二版,图3.1,第243页)显示了<=4点的未标记偏序集。
还有具有n个点的未标记T_0拓扑的数量。例如,a(4)=16拓扑的非同构代表是:
{}{1}{12}{123}{1234}
{}{1}{2}{12}{123}{1234}
{}{1}{12}{13}{123}{1234}
{}{1}{12}{123}{124}{1234}
{}{1}{2}{12}{13}{123}{1234}
{}{1}{2}{12}{123}{124}{1234}
{}{1}{12}{13}{123}{124}{1234}
{}{1}{2}{12}{13}{123}{124}{1234}
{}{1}{2}{12}{13}{123}{134}{1234}
{}{1}{2}{3}{12}{13}{23}{123}{1234}
{}{1}{2}{12}{13}{24}{123}{124}{1234}
{}{1}{12}{13}{14}{123}{124}{134}{1234}
{}{1}{2}{3}{12}{13}{23}{123}{124}{1234}
{}{1}{2}{12}{13}{14}{123}{124}{134}{1234}
{}{1}{2}{3}{12}{13}{14}{23}{123}{124}{134}{1234}
{}{1}{2}{3}{4}{12}{13}{14}{23}{24}{34}{123}{124}{134}{234}{1234}
(结束)
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