Prove Lemma 4.30. (Hint: remember to use the fact that \$$\mathcal{V} is skeletal.) [Previous](https://forum.azimuthproject.org/discussion/2239) [Next](https://forum.azimuthproject.org/discussion/2241) **Lemma 4.30** Serial composition of profunctors is associative: given profunctors \\( \Phi : \mathcal{P} \rightarrow \mathcal{Q} \$$,
\$$\Psi : \mathcal{Q} → \mathcal{R} \$$, and
\$$\Upsilon : \mathcal{R} → \mathcal{S} \$$, we have
$(\Phi.\Psi).\Upsilon = \Phi.(\Psi.\Upsilon)$