设A ={a,b,c,d},B = {1,2,3,4},A到B的关系R = {< b ,4 >, < b ,1 >, < d ,2 >} ,B到A的关系s = {< 4,a>, <2 ,b >, < 3 ,b >},则 = __________
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设A ={a,b,c,d},B = {1,2,3,4},A到B的关系R = {< b ,4 >, < b ,1 >, < d ,2 >} ,B到A的关系s = {< 4,a>, <2 ,b >, < 3 ,b >},则 = __________
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