Closure (Topology)/Examples/Union of Singleton with Open Interval

Example of Closure in the context of Topology
Let $\R$ be the set of real numbers.

Let $H \subseteq \R$ be the subset of $\R$ defined as:
 * $H = \set 0 \cup \openint 1 2$

Then the closure of $H$ in $\R$ is:
 * $H^- = \set 0 \cup \closedint 1 2$