Real Analysis/Limit Points (Accumulation Points)

Definition

Let $(X,d)$ be a metric space, and let $A\subset X$. We call $x\in X$ a limit point of $A$ if for any $ϵ>0$ there exists some $y\ne x$ such that $y\in B(x,ϵ)\cap A$.

We denote the set $lim(A)$ the set of all $x\in X$ such that $x$ is a limit point of $A$.