Observe from the table for A4 given in Table 5.1 on page 111 that the subgroup given in...

Observe from the table for A₄ given in Table 5.1 on page 111 that the subgroup given in Example 9 of this chapter is the only subgroup of A₄ of order 4. Why does this imply that this subgroup must be normal in A₄? Generalize this to arbitrary finite groups.