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Results tagged with algebraic-groups
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user 20787
Algebraic varieties with group operations given by morphisms, or group objects in the category of algebraic varieties, the category of algebraic schemes, or closely related categories.
1
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Examples of discrete subgroups of $PSL_2(\mathbf{R})$ with finite covolume and which are not...
By playing off traces versus Dehn-Thurston coordinates, easy constructions arise.
As suggested in the comments by @YCor, a matrix representation can be written down without much trouble when expresse …
- 15.4k
18
votes
Subgroups of $SL_2(\mathbb R)$ which contain $SL_2(\mathbb Z)$ as a finite index subgroup
$G = SL_2(\mathbb{Z})$ is indeed the only possibility. This follows from the structure of the quotient orbifold $\mathcal{O} = \mathbb{H}^2 / SL_2(\mathbb{Z})$, which is a once-punctured sphere with a …
- 15.4k