LemmaForanytwoelements2SnfffnotreallyaProofYoucanifyoulikesimplycheckthefourpossiblecasesforfandfForexamplesupposef1andf1ThenapplyingtoPrstchangesittoPAppl ID: 198497
Lemma:Foranytwoelements;2Sn f()=f()f():(notreallya)Proof:Youcan ifyoulike simplycheckthefourpossiblecasesforf()andf().Forexample