(50g) Removing Objects From Lists Quickly

[DavidM]

So...

Union seems fairly straightforward, and in this case would be functionally similar to "+ LDDUP" (though implemented a bit more efficiently).

Intersection doesn't have a short-and-sweet equivalent, but seems functionally understandable as well (list of unique elements that are in both lists).

Difference may need some clarification, though. Am I correct in assuming that the target here is what is described on this page as the "relative complement"? That would imply that order of arguments is important (ie. "difference" is not commutative).