 For any "x" in "X", let formula_33 and formula_34, where note that both of these elements are formula_35 and formula_36 with formula_37.Then formula_38 and formula_39 are disjoint, and formula_36 is the unique representation of "x" as the difference of disjoint elements that are formula_35.For all "x" and "y" in "X", formula_42 and formula_43.