One thing that’s nice about it is that you can use a positive difference as an array index directly. This is nice when you want to store a function of the “dist

One thing that’s nice about it is that you can use a positive difference as an array index directly. This is nice when you want to store a function of the “distance” between two things, e.g. potential[] = {-10, -5, -3, -2.2, ...}; ... potential[r1-r2]. It also works nicely with modular arithmetic as ‘0-_-0 mentions in their post. More generally this corresponds to the array being a function from the natural numbers to some other values, and this function can only start at zero if the arrays start at zero. But if you want a function that starts at 1, you can just set x[0] = invalid().