Discrete subgroup of $R^n$ must be free abelian group of rank $\leq n$.
82843
Subgroups of $\Bbb{R}^n$ that are closed and discrete
138406
If N and every subgroup of N is normal in G then G/N is abelian .
137691
What are the self-normalizing subgroups of $S_n$?
66169
Ring of order $n$ is isomorphic to $\Bbb Z/n\Bbb Z$, with $n$ square-free
111141
Why is every discrete subgroup of a Hausdorff group closed?
64269
Finding the minimal $n$ such that a given finite group $G$ is a subgroup of $S_n$
148285
Generator of group $D_n$
95378
Known bounds for the number of groups of a given order.
58863
Proof that $A_n$ the only subgroup of $ S_n$ index $2$.
71262
Subgroups of order $9$ isomorphic to $C_3 \times C_3$ in $S_6$
33387
Proof that $n\Bbb Z \leq \Bbb Z$ and are the only subgroups of $\Bbb Z$
124709
Suppose G be a non-abelian group and H,K be two abelian subgroups of G. Then must HK be an abelian subgroup of G?
50762
If $S_n$ has cyclic subgroups of these orders or not?
85677
Is there a free subgroup of rank 3 in $SO_3$?
122335
Abelian $p$-group with unique subgroup of index $p$
14003
$(\mathbb{Z}/2^n \mathbb{Z})^*$ is not cyclic Group for $n\geq 3$
80180
Discrete and compact subset must be finite