MUZ199 is "Inversion A". That's the easy version that allows you to be clever and use a loophole. I liked this loophole, so I made a version that allows you to use it.
MUZ199B is "Inversion B". I've only done it twice and I don't think I can remember my solution, so this is a "do it yourself" puzzle. This one does not allow you to "cheat" and forces you to figure out the actual "inversion". This is the hard version.