Half-Open Real Interval/Examples/Example 1

Example of Half-Open Real Interval
Let $I$ be the unbounded closed real interval defined as:
 * $I := \hointr 1 2$

Then $1 \in I$.

Proof
By definition of open real interval:
 * $I = \set {x \in \R: 1 \le x < 2}$

As $1 \le 1$ it follows that $1 \in I$.