Let \(U\) be a universe. The action of \(\mathord {\textnormal {\textsf {Sh}}}:{(\mathord {\textnormal {\textsf {Topos}}}(U))}^{\mathord {\textnormal {\textsf {op}}}}\simeq \mathord {\textnormal {\textsf {Logos}}}(U)\) on morphisms is also denoted by \(f\mapsto {f}^{*}\). We call \({f}^{*}\) the inverse image of a morphism \(f\) of \(U\)-toposes.