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2d
awarded  Constituent
Dec
17
revised commuting subsets in a group
edited tags
Dec
15
comment Proper action and compactness
It is easy to prove that $X$ is proper because the action is cocompact and proper: any ball is covered by finitely many compact subspaces.
Dec
15
revised Proof of derivative of invertible function
edited body
Dec
14
revised Interesting question regarding linear dependency
added 2 characters in body
Dec
14
revised $a_{n}$ converges and $\frac{a_{n}}{n+1}$ too?
deleted 5 characters in body
Dec
13
revised Gluing of two geodesic space along a proper space is geodesic.
added 7 characters in body; edited tags
Dec
13
answered Gluing of two geodesic space along a proper space is geodesic.
Dec
13
revised Proper action and compactness
added 59 characters in body; edited tags
Dec
13
answered Proper action and compactness
Dec
11
answered on Cayley diagrams
Dec
10
accepted Is a $0$-hyperbolic group free?
Dec
8
awarded  Caucus
Dec
8
comment Direct product of groups and isomorphism
@WimC: Vipul Naik found a completely elementary proof I find really nice. I described it there: math.stackexchange.com/a/427640/36434
Dec
6
comment How to show the standard $n$-simplex is homeomorphic to the $n$-ball
It is pretty clear on a figure, but you can use the following argument: $\partial \Delta^n$ consists in the intersections of $\Delta^n$ with the hyperplanes $x_i=0$. Because $c$ does not belong to any of these hyperplanes, any ray starting from $c$ can meet $\partial \Delta^n$ at most once, and in fact exactly once since $c \in \Delta^n$.
Dec
6
revised Why do torsion-free abelian groups admit linear orders?
edited tags
Dec
6
answered Why do torsion-free abelian groups admit linear orders?
Dec
6
comment Topological Space with Given Fundamental Group
@MikeMiller: Therefore, any subgroup of $\pi_1(M)$, not necessarily finitely-presented, will work. In that way, we deduce from Higman's embedding theorem that any recursively presented group can be represented as the fundamental group of a (possibly open) manifold of dimension at least four.
Dec
5
comment Cancellation of Direct Product in Top
This could answer your question: math.stackexchange.com/questions/384288/…
Dec
4
answered Evaluate $\displaystyle \lim_{n\to \infty}\sqrt[n]{n!}$