M={1},N={1,2}
A={(x,y)|xâM,yâN}={(1,1),(1,2)}
B={(x,y)|xâN,yâM}={(1,1),(2,1)}
æ以AâªB={(1,1),(1,2),(2,1)}
Aâ©B={(1,1)}
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追é®{(1,1),(1,2)}è¿ä¸ªè¦æä¹è§£éå
追çA={(x,y)|xâM,yâN}={(1,1),(1,2)}
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å 为xâM,说æxåªè½çäº1
yâN,说æyå¯ä»¥çäº1æ2