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11 votes
2 answers
3k views

Why are $S$-arithmetic groups interesting?

Let $K$ be a number field and $S$ a finite set of valuations of $K$, including $\infty$. Define the $S$-numbers $K_S$ to be the direct product $\prod_{s \in S} K_s$ where $K_s$ denotes the completion ...
user14211's user avatar
  • 349
5 votes
3 answers
448 views

Variation of centraliser in $\operatorname{GL}(n,\mathbb{Z})$

$\DeclareMathOperator\GL{GL}$Let $n$ be a positive integer $\geq 2$. The setting is that $K \in \GL(n,\mathbb{Z})$, and people are interested in understanding the centralizer: $$ C(K)=\{ B \in \GL(n,\...
en kuo's user avatar
  • 145