Compact Subset of Hilbert Sequence Space is Closed

Theorem
Let $A$ be the set of all real sequences $\left\langle{x_i}\right\rangle$ such that the series $\displaystyle \sum_{i \mathop \ge 0} x_i^2$ is convergent.

Let $\ell^2 = \left({A, d_2}\right)$ be the Hilbert sequence space on $\R$.

Let $H$ be a compact subset of $\ell^2$

Then $H$ is closed in $\ell^2$.

Proof
From Metric Space fulfils all Separation Axioms, $\ell^2$ is a Hausdorff space.

The result follows from Compact Subspace of Hausdorff Space is Closed.