Librarian can sell Density books

I was casually resetting the Librarian when I got a Density V book trade. I know it's scrapped from the Enchantment Table, and should only be obtained by unlocking an Ominous Vault. To recreate this, simply cross your fingers, get a Librarian and reset it 'till you get a Density book. I think I've got Wind Burst coming as well.