Definition:Accumulation Point/Set

Definition
Let $T$ be a topological space.

Let $A \subseteq T$.

Let $x \in T$.

$x$ is an accumulation point of $A$ :
 * $x \in \operatorname{cl} \left({A \setminus \left\{{x}\right\}}\right)$

where $\operatorname{cl}$ denotes the (topological) closure of a set.