Nonuniform two-intersecting family bound
= Nonuniform two-intersecting family bound
On an even ground set $n=2h$, a <two-intersecting family> has size at most $\sum_{j=h+1}^n\binom nj$. On an odd ground set $n=2h+1$, the bound is $\binom{2h}{h+1}+\sum_{j=h+2}^n\binom nj$. Pair lower levels with complements of upper levels using the <intersecting shadow lemma>; apply the <Erdős-Ko-Rado theorem> to the remaining middle level in the odd case.