Boundary (Topology)/Examples/Open Unit Interval

Examples of Boundaries in the context of Topology
Let $\struct {\R, \tau_d}$ be the real number line with the usual (Euclidean) topology. Let $\openint 0 1$ be the open unit interval in $\R$.

Then the boundary of $\openint 0 1$ is the set of its endpoints $\set {0, 1}$.