Consider the set $(-\infty, 0]\cup\{1/n:n\in\mathbb{N}\}$ with the subspace topology. Then
- $0$ is an isolated point
- $(–2, 0]$ is an open set
- $0$ is a limit point of the subset $\{1/n:n\in\mathbb{N}\}$
- $(–2, 0)$ is an open set.
I think 3 and 4 are correct.am I right?