Definition:Direct Image of Presheaf/Definition 1

Definition
Let $\mathbf C$ be a category.

Let $T_1 = \struct {S_1, \tau_1}$ and $T_2 = \struct {S_2, \tau_2}$ be topological spaces.

Let $f: T_1 \to T_2$ be continuous.

Let $\FF$ be a $\mathbf C$-valued presheaf on $T_1$.

The direct image of $\FF$ via $f$ is the $\mathbf C$-valued presheaf $f_* \FF$ on $T_2$ with:


 * $\map {f_* \FF} V = \map \FF {f^{-1} \sqbrk V}$ for all open set $V$ of $T_2$


 * Restrictions $\operatorname{res}^U_V = \operatorname{res}^{f^{-1} \sqbrk U}_{f^{-1} \sqbrk V}$

Also see

 * Equivalence of Definitions of Direct Image of Presheaf