Definition:Bounded Below Set

This page is about Bounded Below in the context of Ordered Set. For other uses, see Bounded Below.

Definition

Let $\struct {S, \preceq}$ be an ordered set.

A subset $T \subseteq S$ is bounded below (in $S$) if and only if $T$ admits a lower bound (in $S$).

The concept is usually encountered where $\struct {S, \preceq}$ is the set of real numbers under the usual ordering $\struct {\R, \le}$:

A subset $T \subseteq \R$ is bounded below (in $\R$) if and only if $T$ admits a lower bound (in $\R$).

Let $\struct {S, \preceq}$ be an ordered set.

A subset $T \subseteq S$ is unbounded below (in $S$) if and only if it is not bounded below.