\begin{definition}[Definition:Real Interval/Singleton]
Let $a, b \in \R$.
Consider the closed interval $\closedint a b \subseteq \R$.
When $a = b$:
:$\closedint a b = \closedint a a = \set {x \in \R: a \le x \le a} = \set a$
Such an interval is sometimes referred to as a '''singleton interval'''.
\end{definition}