Continuous Linear Transformation Algebra with Supremum Operator Norm is Normed Algebra

Theorem

Let $\struct {X, \norm {\, \cdot \,}_X}$ be a normed vector space.

Let $\map {CL} X := \map {CL} {X, X}$ be a continuous linear transformation space.

Let $\struct {\map {CL} X, *}$ be an associative algebra.

Let $\norm {\, \cdot \,}$ be the supremum operator norm.

Then $\struct {\struct {\map {CL} X, *}, \norm {\, \cdot \,}}$ is a normed algebra.

Proof

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Sources

• 2017: Amol Sasane: A Friendly Approach to Functional Analysis ... (previous) ... (next): Chapter $\S 2.4$: Composition of continuous linear transformations