FYI, the books don't transform into bookshelves. Maybe I don't understand how the interaction is supposed to work, but the books are just self-destructing without adding any bookshelves into my militia.
Great game otherwise!
Edit: I got a bookshelf, so it does work, but I'm still not sure why it only worked after destroying around 8 books.
Second Edit: the book strategy feels extremely weak. You need the writer, who deals 0 damage to generate a bunch of books. The books also deal 0 damage, and you need them to generate a bookshelf. And then the bookshelf, finally... deals 0 damage but increases the damage of your librarians! I haven't even found a single librarian yet! The strategy requires you to jump through a lot of loops for a very strange payoff.