Derived set (mathematics)

In mathematics, more specifically in point-set topology, the derived set of a subset ${\displaystyle S}$ of a topological space is the set of all limit points of ${\displaystyle S.}$ It is usually denoted by ${\displaystyle S'.}$

The concept was first introduced by Georg Cantor in 1872 and he developed set theory in large part to study derived sets on the real line.