证明有定义知H包含于G1对于任意的a,b∈H,有f(a)=g(a),f(b)=g(b)∵f和g都是同态映射,所以必有f(b－¹)=f(b)－¹,g(b－¹)=g(b)－¹现因f(b)=g(b),故有f(b)－¹=g(b)－¹即有f(b－¹）=...