Definition:Final Topology/Definition 1

Definition
Let $X$ be a set.

Let $I$ be an indexing set.

Let $\family {\struct{Y_i, \tau_i}}_{i \mathop \in I}$ be an $I$-indexed family of topological spaces.

Let $\family {f_i: Y_i \to X}_{i \mathop \in I}$ be an $I$-indexed family of mappings.

The final topology on $X$ with respect to $\family {f_i}_{i \mathop \in I}$ is defined as:
 * $\tau = \set{U \subseteq X: \forall i \in I: f_i^{-1} \left({U}\right) \in \tau_i} \subseteq \map {\mathcal P} {X}$

Also see

 * Equivalence of Definitions of Final Topology