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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.
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
1
vote
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