问题7：为什么我们在正规子群概念下讨 论商群？ Normal Subgroups A subgroup H of a group G is normal in G if gH=Hg for all g EG.That is,a normal subgroup of a group G is one in which the right and left cosets are precisely the same. Theorem 10.2 Let N be a normal subgroup of a group G.The cosets of N in G form a group G/N of order [G:N].问题7：为什么我们在正规子群概念下讨 论商群？