Example 9.2.2.14. Let $\operatorname{\mathcal{C}}$ be an $\infty $-category and let $W$ be the collection of all isomorphisms in $\operatorname{\mathcal{C}}$. It follows from Corollary 9.2.2.12 and Example 9.2.2.7 that $W$ is the smallest collection of morphisms of $\operatorname{\mathcal{C}}$ which is closed under transfinite composition: that is, it is the transfinite closure of the empty set.
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