The set of complex values is the unit disk.

Considered as a Riemann surface, the open unit disk is therefore different from the complex plane.

Let D be the unit disk in the complex numbers.

It follows that the critical points must be within the unit disk, since the roots are.

Consequently the point spectrum of "T" contains the open unit disk.

Any such is diffeomorphic to the closed unit disk.

In particular, the open unit disk is homeomorphic to the whole plane.

One also considers unit disks with respect to other metrics.

The resulting point will not lie on the unit disk.

Now let us take some figure such as the unit square or the unit disk.