 If "x" and "y" are disjoint then formula_22 and formula_23, where for any element "z", formula_24 and formula_25.We say that two sets "A" and "B" are disjoint if "a" and "b" are disjoint for all "a" in "A" and all "b" in "B", in which case we write formula_26.If "A" is the singleton set formula_27 then we will write formula_28 in place of formula_29.