Definition 8.3.2.18 (Balanced Profunctors). Let $\operatorname{\mathcal{C}}_{-}$ and $\operatorname{\mathcal{C}}_{+}$ be $\infty $-categories. We say that a profunctor $\mathscr {K}: \operatorname{\mathcal{C}}_{-}^{\operatorname{op}} \times \operatorname{\mathcal{C}}_{+} \rightarrow \operatorname{\mathcal{S}}$ is balanced if it satisfies the following conditions:
The profunctor $\mathscr {K}$ is representable and corepresentable (Definition 8.3.2.9).
Let $X$ be an object of $\operatorname{\mathcal{C}}_{-}$, let $Y$ be an object of $\operatorname{\mathcal{C}}_{+}$, and let $\eta $ be a vertex of the Kan complex $\mathscr {K}(X,Y)$. Then $\eta $ is universal if and only if it is couniversal.