What has the author Constantine Fettel written?

There is no widely recognized author named "Constantine Fettel." It is possible that you are thinking of a different name, or that this is a pseudonym.

To help me identify the author you are looking for, could you provide more context? For example:

* Is there a specific book or work you are interested in?

* Do you have any other information about the author, like their genre or approximate time period of their writing?

With more information, I might be able to help you find the author you are looking for.