What has the author Robert Jones Derfel written?

There is no author by the name of "Robert Jones Derfel" listed in any major literary database. It's possible that:

* The name is misspelled: Double-check the spelling. Perhaps it's a slightly different name.

* The author is relatively unknown: If the author is new or publishes in a niche genre, their work might not be widely indexed.

* It's a pseudonym: The author might use a pen name.

Could you please provide more information, such as:

* Any other details about the author's work: Genre, time period, any specific titles or themes.

* Where you encountered the name: A book, online article, or other source.

With more details, I can help you find information about the author.