public static <A> Douce<Set<A>,Set<A>> getDiffs(Collection<A> col1, Collection<A> col2) {
		HashSet<A> diff1 = new HashSet<A>(col1);
		Set<A> set2 = toSet(col2);
		HashSet<A> diff2 = new HashSet<A>();
		for (A a : set2) {
			if (diff1.remove(a)) {
				; // Both contain this element, simply remove
			} else {
				// Only col2 contain this element, add to diff2 set
				diff2.add(a);
			}
		}
		return new Douce<Set<A>,Set<A>>(diff1, diff2);
	}