\begin{definition}[Definition:Real Interval/Unit Interval/Closed]
The closed interval from $0$ to $1$ is denoted $\mathbb I$ (or a variant) by some authors:
:$\mathbb I := \closedint 0 1 = \set {x \in \R: 0 \le x \le 1}$
This is often referred to as the '''closed unit interval'''.
\end{definition}