We have even/odd, high/low, so why not try something different.

Set one ("open" numbers) = 1, 2, 3, 5 and 7

Set two ("Closed" numbers) = 0, 4, 6, 8 and 9

Why? Why not?

The open numbers have no enclosed loops, the closed numbers each have 1 enclosed loop, but 8 has 2.

Mixes up vs. High/Low and Even/Odd... could even pair them up like mirrors etc...

Inverted...

1   9

2   8

3   6

5   4

7   0

Have fun...