[Semaphor]

> You should filter out authors from the input books in the output.

No, or at least make it configurable.

I’d agree for series, but not for Authors, just because I once read a book by someone doesn’t mean I even know they have other stuff, the list of Authors I read and enjoyed is very long.

[blehn]

Configurability is fine, but it's too obvious a recommendation and just creates noise. The purpose of a recommendation system is to help you find things that aren't obvious. I'd still filter them out by default even if it's configurable.