you take an altar, dark enchanter and an infusion table, you take an enchanted book, lets just use sharpness as an example for now, you take a sharp 5 book and put it on a wood sword, then you take it to the altar, you make it sharpness 6, but oh no theres a curse on it now, then you go to the dark enchanter and just remove the curse for absolutely free, but oh no, you cant use the altar again?? just slap a book, ur sword on an infusion table, use a flint and steel on it and bam, you have a sharpness 6 book.. so then if you keep repeating this process but with the upgraded book.. you can get insane enchant levels