= Kuratowski ordered pair
{c}
{title2=$\langle a,b\rangle=\{\{a\},\{a,b\}\}$}
This representation of an <ordered pair> by <sets> satisfies $\langle a,b\rangle=\langle c,d\rangle$ exactly when $a=c$ and $b=d$. Its intersection recovers $\{a\}$, and its union recovers $\{a,b\}$; if the latter is a singleton then $b=a$. Its <rank of a set> is $\max(\operatorname{rank}(a),\operatorname{rank}(b))+2$, which bounds the ranks of <function> graphs in <absoluteness of cardinalhood in limit ranks>.
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