Definition:Supremum of Mapping/Real-Valued Function/Definition 2

Definition
Let $f: S \to \R$ be a real-valued function.

Let $f$ be bounded above on $S$.

The supremum of $f$ on $S$ is defined as $\displaystyle \sup_{x \mathop \in S} f \left({x}\right) := K \in \R$ such that:


 * $(1): \quad \forall x \in S: f \left({x}\right) \le K$
 * $(2): \quad \exists x \in S: \forall \epsilon \in \R_{>0}: f \left({x}\right) > K - \epsilon$

Also see

 * Equivalence of Definitions of Supremum of Real-Valued Function