Closed subset of a affine linear group
92064
A closed subset of an algebraic group which contains $e$ and is closed under taking products is a subgroup of $G$
142228
Proof that a subset closed under group operation of a finite group is a subgroup
122271
A subset of a transitive set is transitive
64269
Finding the minimal $n$ such that a given finite group $G$ is a subgroup of $S_n$
98474
Show the existence of a certain subgroup of F2
99678
Is a sphere a closed set?
81543
Finite abelian group contains an element with order equal to the lcm of the orders of its elements
58925
Order of general linear group of $2 \times 2$ matrices over $\mathbb{Z}_3$
108740
$C^1[a,b]$ is closed in $C[a,b]$
111049
Groups with given automorphism groups
112407
Set of left cosets is a group
31696
Strongly complete profinite group
93666
Does the closedness of a subgroup $H$ of $G$ imply that for $h\in H, g\in G \setminus H : hg \not \in H$?
17510
Proving a set is an abelian group.
3462
Proving a set of automorphisms of a group is a group under composition
158569
Proving a particular subset of $R^n$ is closed
49374
Closure of a subset in a metric space