Let $G$ be a Lie group and $T \subset G$ a torus, show that $N(T)$ is a closed subgroup of $G$. Could somebody give a sketch of the proof?
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Say $n_i\in N(T)$ converges to $n$, and let $t\in T$. Then $$n_itn_i^{-1}\rightarrow ntn^{-1}.$$ Since $n_itn_i^{-1}\in T$ we have $ntn^{-1}\in T$ since $T$ is closed.
Rene Schipperus
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thanks for the answer! So the key is $T$ is closed, which is true because of its monogenicity, right? – PhysicsMath Sep 26 '16 at 01:56
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Yeah, it seem to hold for any closed subgroup. Sorry, I cant remember what monogenicity means at the moment. – Rene Schipperus Sep 26 '16 at 01:59