I accidentally updated my "The Swift Programming Language" book to the Swift 4 edition from Swift 3.1. Can I revert back to 3.1?
If you use Time Machine and iCloud for your iBooks you could look here:
The path is only accessible via Terminal, so type in Terminal.App:
open ~/Library/Mobile\ Documents/iCloud\~com\~apple\~iBooks/Documents
This will open a Finder window with all your iBooks in it. Use this window to start Time Machine.
Please note: I’m not sure if that folder is part of a default backup.