corollary of Banach-Alaoglu theorem
Corollary.
A Banach space is isometrically isomorphic to a closed subspace of for a compact
Hausdorff space .
Proof.
Let be the unit ball of . By the Banach-Alaoglu theorem it is compact in the weak- topology. Define the map by . This is linear and we have for :
With the Hahn-Banach theorem it follows that there is a such that . Thus and is an isometric isomorphism, as required.∎