Kerodon

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Remark 1.3.6.3 (Two-out-of-three). Let $f: X \rightarrow Y$ and $g: Y \rightarrow Z$ be morphisms in an $\infty$-category $\operatorname{\mathcal{C}}$ and let $h$ be a composition of $f$ and $g$. If any two of the morphisms $f$, $g$, and $h$ is an isomorphism, then so is the third.