 Banach–Stone theorem

A surjective linear isometry $U:C(K)\to C(L)$ between compact Hausdorff function spaces has the form $(Uf)(s)=u(s)f(h(s))$, where $h:L\to K$ is a homeomorphism and $u$ is continuous with modulus one. Thus the Banach space structure of $C(K)$ determines $K$ up to homeomorphism.

The Banach–Stone theorem is a fundamental result in functional analysis that provides a characterization of certain types of continuous linear operators between spaces of continuous functions. Specifically, it deals with the relationship between spaces of continuous functions on compact Hausdorff spaces.