Difference is not an associative operation though. E.g.
A.difference(B, C, D) means A - B - C - D
which can be (((A - B) - C) - D)
or (((A - D) - C) - B)
or (((A - C) - B) - D)
or (((A - C) - D) - B)
You can do the subtractions from A in any order.
Raymond
