Definition:Interval/Open Interval

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Let $\left({S, \preceq}\right)$ be a totally ordered set.

Let $a, b \in S$.

Open Interval on Ordered Set

The open interval between $a$ and $b$ is the set:

$\openint a b := a^\succ \cap b^\prec = \set {s \in S: \paren {a \prec s} \land \paren {s \prec b} }$


$a^\succ$ denotes the strict upper closure of $a$
$b^\prec$ denotes the strict lower closure of $b$.

Open Real Interval

In the context of the real number line $\R$:

The open (real) interval from $a$ to $b$ is defined as:

$\openint a b := \set {x \in \R: a < x < b}$

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