Stack Exchange network consists of 177 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Q&A for work
Connect and share knowledge within a single location that is structured and easy to search.
Both tags, book and books refer to the same thing and thus should be merged. As stated in this comment: Merge 'formula' and 'formulas' probably they should be merged to books.
This has been done and a synonym created for book > books