Definition:Supremum Norm/Continuous on Closed Interval Real-Valued Function

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Let $I = \closedint a b$ be a closed real interval.

Let $\map C I$ be the space of real-valued functions continuous on $I$.

Let $f \in \map C I$.

Let $\size {\, \cdot \,}$ denote the absolute value.

Suppose $\sup$ denotes the supremum of real-valued functions.

Then the supremum norm over $\map C I$ is defined as

$\ds \norm {f}_\infty := \sup_{x \mathop \in I} \size {\map f x}$