I am trying to find $ S' $ for function S:{ r $\in Q$ , $ 0<r\le\sqrt2$ }
Now I believe that $S'={\{0,\sqrt2\}}$ and isolation point is ${\{1}\}$ Now my understanding for this answer is that since $\sqrt2\ $is a irrational number it could never be a part of $S$, also for isolation any $x\in S$ and $x\notin S'$ is isolation. Is this the correct approach