not a neat partition right so so there are actually a lot of choices for this so this particular choice is true is it so that it's very easy to implement the encoding and decoding operations so you can just do it with some modular um but if you have some crazy choice maybe it'll work but it might be very hard to to compute B encode and decode operations well it seems like the set of natural number that is also chosen like can be chosen otherwise here like we don't have to we only restrict a natural number because of the index is zero so