Let \(X\) be a topological space and \(A\subseteq X\). A point \(p\in A\) is an isolated point of \(A\) if \(p\) is not a limit point of \(A\).
A point \(p\in A\) is an isolated point of \(A\) if and only if there is a neighborhood \(U\) of \(p\) with \(U\cap A = \ts{p}\).