> 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