Space of Bounded Linear Transformations is Banach Space

Theorem
Let $H, K$ be Hilbert spaces, and let $B \left({H, K}\right)$ be the space of bounded linear transformations from $H$ to $K$.

Let $\Bbb F \in \left\{{\R, \C}\right\}$ be the ground field of $K$.

Now $B \left({H, K}\right) \subseteq K^H$, the set of mappings from $H$ to $K$.

Therefore, $B \left({H, K}\right)$ can be endowed with pointwise addition ($+$) and ($\Bbb F$)-scalar multiplication ($\circ$).

Let $\norm{\,\cdot\,}$ denote the norm on bounded linear transformations.

Then $\norm{\,\cdot\,}$ is a norm on $B \left({H, K}\right)$.

Furthermore, $B \left({H, K}\right)$ is a Banach space with respect to this norm.