how do i remove a book from my ibook library?

Hi, amato.bob!

Thanks so much for using the Apple Support Communities. After reading your post, I understand your question is if it's possible to remove books from you have purchased from your iBooks library, and if so, how. I can definitely appreciate wanting to clear up your library, and am happy to provide you with some information!

All of your purchases from the iBooks Store (as well as the App Store and the iTunes Store) are permanently associated with your Apple ID. While you are able to hide those purchases so you no longer see them in your library, they cannot be removed from your purchase history entirely. The article linked below will guide you through how to hide your purchases.
Hide and unhide iTunes Store, App Store, or iBooks Store purchases

Have a lovely day!