Shouldn't it be like , if A and B have one element in common then , n {(AxB) intersection (BXA)} also be one and if A and B have 2 elements in common then , n {(AxB) intersection (BXA)} be 2 and like wise for 3 ,4,5 ... But it's given that if A and B have 3 elements in common then , n {(AxB) intersection (BXA)}=9 How is this possible , we don't repeat same elements in the intersection of sets . Please someone explain clearly .

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