Variant 4.2.2.2 (Right Anodyne Morphisms). Let $T_{R}$ be the smallest collection of morphisms in the category $\operatorname{Set_{\Delta }}$ with the following properties:
For each $n > 0$ and each $0 < i \leq n$, the horn inclusion $\Lambda ^{n}_{i} \hookrightarrow \Delta ^ n$ belongs to $T_{R}$.
The collection $T_{R}$ is weakly saturated (Definition 1.4.4.15). That is, $T_{R}$ is closed under pushouts, retracts, and transfinite composition.
We say that a morphism of simplicial sets $f: A \rightarrow B$ is right anodyne if it belongs to $T_{R}$.