Nonuniform t-intersecting family bound
= Nonuniform t-intersecting family bound
{title2=$|\mathcal A|\leq D(n,n-t)$}
If $|A\cap B|\geq t$, then $|A\triangle B|=|A\cup B|-|A\cap B|\leq n-t$. The <Kleitman diametric theorem> therefore gives the sharp nonuniform intersection bound. For $n-t=2q$, all sets of size at least $n-q$ attain it. For $n-t=2q+1$, take all sets of size at least $n-q$, together with all $(n-q-1)$-sets avoiding one fixed point.