Set of Integers Bounded Above by Real Number has Greatest Element

Theorem

Let $\Z$ be the set of integers.

Let $\le$ be the usual ordering on the real numbers $\R$.

Let $\O \subset S \subseteq \Z$ such that $S$ is bounded above in $\struct {\R, \le}$.

Then $S$ has a greatest element.

Proof

Let $S$ be bounded above by $x \in \R$.

By the Axiom of Archimedes, there exists an integer $n \ge x$.

Then $S$ is bounded above by $n$.

By Set of Integers Bounded Above by Integer has Greatest Element, $S$ has a greatest element.

$\blacksquare$

Also see

• Set of Integers Bounded Above has Greatest Element
• Set of Integers Bounded Below by Real Number has Smallest Element