Prove that A_3 inside S_3 is normal.
To prove this use the definition that if a group is normal then as a collection left cosets equal right cosets.
I used S_3 to equal a symmetric triangle with {1,l,r,a,b,c} A_3 the group of even permutations in S_3 which are {1,l,r}
Right Cosets Left Cosets
A_3 * 1 1 * A_3
--Robertsr 19:58, 1 October 2008 (UTC)