Precedence of set union, intersect, and difference? Online, I have read contradicting opinions on whether `intersect` should take precedence over `union` (by analogy to logical `and` and `or`), or whether all set operators should have equal precedence. Which way makes more sense and why? And where does `difference` fit in? (I'd say it should be equal precedence to `intersect` because `A - B = A intersect B'`.)

There is no sensible way of preferring one of intersection and union more than the other, since complement switches them. I don't think you should assume an order at all and you should always use parentheses.