Is there a simple way to to identify and remove matching pairs from 2 lists? For example: I have a=[2, 5, 3, 4, 7, 2, 2, 4, 8, 1] b=[7, 3, 5, 8, 1, 7, 4, 8, 2, 6] and I want to get this: a=[2, 5, 3, 4, 7, 2, 8, 1] b=[7, 3, 5, 8, 1, 4, 2, 6] There are recurring pairs of (2, 7) and (4, 8), and so I want to remove one of each pair. Many thanks, Evan