Suppose a function of a complex variable $z$ is defined as:
Then $f$ is analytic in every open set such that the sum converges in the set.
To discuss it in more detail, feel free to use the talk page.
When this page/section has been completed, {{Stub}} should be removed from the code.
If you would welcome a second opinion as to whether your work is correct, add a call to {{Proofread}} the page (see the proofread template for usage).