Prove Lemma 4.30. (Hint: remember to use the fact that \\( \mathcal{V} is skeletal.)

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**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
\[ (\Phi.\Psi).\Upsilon = \Phi.(\Psi.\Upsilon) \]