`difference` is actually `relativeComplement`

[robrix]

The symmetric difference of sets a and b is (a + b) - (a & b) (the union minus the intersection). difference() is actually doing the equivalent of a - b which is the relative complement of b in a.

We should rename difference to complement or relativeComplement and implement a real symmetric difference method.

cf #4.

[sharplet]

Voting for complement, as opposed to relativeComplement, which I think implies it's the relative kind due to the types involved. We don't have a useful idea of a "universe" to absolutely complement with respect to.

[robrix]

That’s my thinking as well 👍