Artificial intelligent assistant

Locally compact infinite dihedral group Is there any topology other than discrete which can be given to an infinite dihedral group to make it locally compact topological group? If no, why is it so?

If you require that the group be Hausdorff then the answer is No. In fact this is true of any countable group. Here is a proof.

Let $G$ be a countable group. Assume that it does not have the discrete topology. This means that there is some element $g\in G$ such that for any open neighborhood $\mathcal{O}_g$ with $g\in \mathcal{O}_g$ there is a point $h\
eq g$ with $h\in\mathcal{O}_g$. So in particular $g$ is a limit point. Since group multiplication is a homeomorphism you get that every element of the group is a limit point.

Now since the group is locally compact it is a Baire space, since it is Hausdorff then sets of the form $\mathcal{K}_g=G\setminus \\{g\\}$ are open (ie points are closed) and by the previous paragraph they are also dense.

Thus by Baire category we get that $\cap_{g\in G}\mathcal{K}_g=\emptyset$ is dense, which is a contradiction.

Of course if you do not require Hausdorff then you can put the trivial topology on any set.

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