Definition:Quotient Topology/Definition 1

Definition
Let $T = \left({S, \tau}\right)$ be a topological space.

Let $\mathcal R \subseteq S \times S$ be an equivalence relation on $S$.

Let $q_\mathcal R: S \to S / \mathcal R$ be the quotient mapping induced by $\mathcal R$.

Let $\tau_\mathcal R$ be the identification topology on $S / \mathcal R$ by $q_\mathcal R$:
 * $\tau_\mathcal R := \left\{{U \subseteq S / \mathcal R: q_\mathcal R^{-1} \left({U}\right) \in \tau}\right\}$

Then $\tau_\mathcal R$ is the quotient topology on $S / \mathcal R$ by $q_\mathcal R$.

Also see

 * Identification Topology
 * Identification Topology equals Quotient Topology on Induced Equivalence