  We provide a necessary condition for the existence of a 3-point holomorphic
interpolant $F:\mathbb{D}\longrightarrow\Omega_n$, $n\geq 2$. Our condition is
inequivalent to the necessary conditions hitherto known for this problem. The
condition generically involves a single inequality and is reminiscent of the
Schwarz lemma. We combine some of the ideas and techniques used in our result
on the $\mathcal{O}(\mathbb{D},\Omega_n)$-interpolation problem to establish a
Schwarz lemma -- which may be of independent interest -- for holomorphic
correspondences from $\mathbb{D}$ to a general planar domain $\Omega\Subset
\mathbb{C}$.
