Hm, this isn't easy.
A set of numbers:
A = {1, 2, 3, 4, 5, 6, 7, 8, 9}
Permutations of this set will look like:
1 2 3 4 5 6 7 8 9
2 1 3 4 5 6 7 8 9
2 1 4 3 5 6 7 8 9
8 9 1 2 3 4 5 6 7
Let's order these permutations like this:
(x_1, x_2), (x_3, x_4), (x_5, x_6), x_7, x_8, x_9
We...