Trace of a set family
= Trace of a set family
{title2=$T_F(\mathcal A)$}
For a set family $\mathcal A\subseteq\mathcal P([n])$ and $F\subseteq[n]$, its trace on $F$ is
$$
T_F(\mathcal A)=\{A\cap F:A\in\mathcal A\}.
$$
= Trace of a set family
{title2=$T_F(\mathcal A)$}
For a set family $\mathcal A\subseteq\mathcal P([n])$ and $F\subseteq[n]$, its trace on $F$ is
$$
T_F(\mathcal A)=\{A\cap F:A\in\mathcal A\}.
$$