1. ## Normal subgroup

An Normal subgroup of Sn?
why??

2. Originally Posted by cvcv49
An Normal subgroup of Sn?
why??

Proof 1: because $[S_n:A_n]=2$ ;

Proof 2: because $\pi^{-1}\sigma\pi\in A_n\,\,\,\forall\,\pi\in S_n\,\,\forall \sigma\in A_n$

Tonio

3. And also a trivial one and $S_n$ itself