> 怎样理解这句话呢？怎么感觉是自相矛盾的阿。
> 
>  and in each group, one object is at least X resemble to another object in the same group, i.e, for every object i, if i is not the only member of the group, then there exists one object j (i ≠ j) in the same group that satisfies dij < X