  We prove some properties of the Kruskal-Katona function, and apply to the
following variation of cross-intersecting antichains. Let $n\ge 4$ be an even
integer and $\mathscr{A}$ and $\mathscr{B}$ be two cross-intersecting
antichains of $\mathbb{N}_n$ with at most $k$ disjoint pairs, i.e. for all
$A_i\in \mathscr{A}$, $B_j\in\mathscr{B}$, $A_i\cap B_j=\emptyset$ only if
$i=j\le k$. We prove a best possible upper bound on
$|\mathscr{A}|+|\mathscr{B}|$. Furthermore, we show that the extremal families
contain only $\frac{n}{2}$ and $(\frac{n}{2}+1)$-sets.
