• Interaction With Direct Images. Let $f\colon X\to Y$ be a map of sets. The diagram

    commutes, i.e. we have

    \[ \bigcup _{U\in \mathcal{U}}f_{*}\webleft (U\webright )=\bigcup _{V\in f_{*}\webleft (\mathcal{U}\webright )}V \]

    for each $\mathcal{U}\in \mathcal{P}\webleft (X\webright )$, where $f_{*}\webleft (\mathcal{U}\webright )\mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}\webleft (f_{*}\webright )_{*}\webleft (\mathcal{U}\webright )$.


Noticed something off, or have any comments? Feel free to reach out!


You can also use the contact form below: