  Let $S$ and $T$ be subsets of $\mathbf{F}_q^n$. We show there are subsets
$S'$ of $S$ and $T'$ of $T$ such that $S+T$ is the union of $S+T'$ and $S'+T$,
with $|S'| + |T'|$ bounded by $c^n$ with $c < q$. The proof relies on the
method of Croot-Lev-Pach and Ellenberg-Gijswijt on the cap set problem,
together with a result of Meshulam on linear spaces of low-rank matrices. The
result is a modest generalization of the recent bounds on (single-colored and
multi-colored) sum-free sets by the author and others.
