Unbounded Closed Real Interval/Examples/Example 1

Example of Unbounded Closed Real Interval
Let $I$ be the unbounded closed real interval defined as:
 * $I := \hointl \gets 3$

Then $2 \in I$.

Proof
By definition of open real interval:
 * $I = \set {x \in \R: x \le 3}$

As $2 \le 3$ it follows that $2 \in I$.