Definition:Set Derivative

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

Let $A \subseteq S$.

The derivative of $A$ in $T$ is the set of all accumulation points of $A$.

It is usually denoted on as $A'$.

Also known as
The set derivative can also be referred to as the derived set.

It can also be denoted $\operatorname{Der} A$.