it's because of the maths: I do feel like the article overcomplicated things a bit: the basic idea is, each individual book is basically a choose-your-own-adven

it's because of the maths: I do feel like the article overcomplicated things a bit: the basic idea is, each individual book is basically a choose-your-own-adventure of flying around a static opposing aircraft. If you pick page numbers yourself you can happily just fly around your 'opponent', who never moves on their own. But, the page numbers for opposing books correspond to the inverse of the move in the other one: so when you take the page number from your opponent, you are doing the inverse of their move on your book (which may not be an option listed on your page). This basically means there are two opposite maps: if you tried to play with two books from the same side it would seem like you are just wrestling over the controls of one plane.