(1)(A-B)={{a,b,},2,},
(2) (A U B)={{a,b,},1,2,a,b,{1}},
(3) (A U B)-(A U(反过来) B) ={{a,b,}1,2,a,b,{1}}-{1} =={{a,b,},2,a,b,{1}}
(1)(A-B)={{a,b,},2,},
(2) (A U B)={{a,b,},1,2,a,b,{1}},
(3) (A U B)-(A U(反过来) B) ={{a,b,}1,2,a,b,{1}}-{1} =={{a,b,},2,a,b,{1}}