Definition 13.1.3 (Interval). Let $(E, \le)$ be an ordered vector space and $x, y \in E$, then
\[[x, y] = \bracs{z \in E| x \le z \le y}\]
is the order interval with endpoints $x$ and $y$.
Definition 13.1.3 (Interval). Let $(E, \le)$ be an ordered vector space and $x, y \in E$, then
is the order interval with endpoints $x$ and $y$.