两个群的内直积 Let G be a group with subgroups H and K satisfying the following conditions. ·G=HK={hk:h∈H,k∈K； 。HnK={e; 。hk=kh for all k∈K and h∈H. Then G is the internal direct product of H and K. Example 9.24.The group U(8)is the internal direct product of H={1,3}andK={1,5}.两个群的内直积