use for 2nd grindstone slot

when you put an item in the 1st slot and an enchanted book in the 2nd slot of a grindstone, the output removes that enchantment from the first item. For example, if you insert a sword with bane of arthropods 5 into the first slot, and a book with that same enchantment, it removes that enchantment from the sword in the output. On the other hand, if the book has bane of arthropods 4, the sword in the output will have bane of arthropods 1.