2g是permutation? For any g∈G,define a function入g:G→Gby入g(a)=ga.We claim thatλgisa permutation of G.To show that Ag is one-to-one,suppose that Ag(a)=Ag(b).Then ga=入g(a)=λg(b)=gb. Hence,a =b.To show that A is onto,we must prove that for each a G,there is a b such that Ag(b)=a.Let b=g-a.𝜆𝑔 是permutation？