Normal subgroup of $A_4$
49257
How to show that Klein four-group is a normal subgroup of the alternating group $A_4$
113013
Let $M$ and $N$ be two normal subgroups of $G$. Show that $M \cap N$ is also normal in $G$. Then show that $G/(M \cap N) \cong (G/M) \times (G/N)$
41688
An elementary problem in Group Theory: the unique noncyclic group of order 4
7108
Normal subgroup of prime index
45277
The alternating group is a normal subgroup of the symmetric group
2767
Subgroups of the Klein-4 Group
28108
Proving the kernel is a normal subgroup.
101079
Inner automorphisms form a normal subgroup of $\operatorname{Aut}(G)$
23533
All subgroups normal $\implies$ abelian group
22632
Galois group of $x^4-2$
74586
Prove that every group of order $4$ is abelian
101360
Why is a normal subgroup of $G_1\times G_2$ with trivial intersections with $G_1$ and $G_2$ is abelian?
133272
Number of normal subgroups of a non abelian group of order $21$... CSIR December $2013$
36040
A Group Having a Cyclic Sylow 2-Subgroup Has a Normal Subgroup.
14611
$A_4$ has no subgroup of order $6$?
45580
Intersection of conjugate subgroups is normal
116628
Example of Galois extension whose Galois group is $A_4$