As many of you will know, there$$s a genre of fantasy$-$themed computer games where there$$s some overall quest or storyline

to follow, and some side$-$quests along the way to flesh out the world and build up power for the grand finale$\mathrm{.}1$ A big

part of those games is the magic system. In the magic system, you learn increasingly powerful spells, but you typically

have to learn the lower$-$level spells before you can attempt the higher$-$level ones$\mathrm{.}2$ Sometimes you$$ll also want to unlearn

some spells too: you get to the final Boss and discover that you actually needed mordenkainens$-$undead$-$platoon$-$summon

rather than divine$-$firestorm.