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Oct 6, 2019 at 4:20 history edited Ami CC BY-SA 4.0
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Oct 6, 2019 at 0:54 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 23:57 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 22:50 history edited LSpice CC BY-SA 4.0
Proofreading
Oct 5, 2019 at 22:41 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 21:02 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 19:47 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 19:47 comment added Ami @YCor yes thanks.
Oct 5, 2019 at 19:37 comment added YCor Since (passing to a smaller finite index subgroup) you can suppose that $G$ is normal in $\mathrm{SO}_6(\mathbf{Z})$ (and hence normalized by $e_{1,1}$), you can write $G$ instead of $A^{-1}GA$ in your new question.
Oct 5, 2019 at 19:34 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 19:11 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 13:41 history edited YCor CC BY-SA 4.0
fixed question (according to answer in comment)
Oct 5, 2019 at 13:35 comment added Ami @YCor Thank you yes I did miss this simple fact as Misha pointed, in regards to the second question I believe that $Be_{1,1}B$ is a Bruhat cell (which is not the big cell)
Oct 5, 2019 at 13:33 history edited Ami CC BY-SA 4.0
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Oct 5, 2019 at 6:01 comment added YCor Clearly $H\cap\mathrm{GL}_6(\mathbf{Z})$ is finite (of cardinal $4$) and does not contain the identity matrix. Hence there is a finite index subgroup with empty intersection with $H$ (e.g., kernel of reduction modulo 2).
Oct 5, 2019 at 5:58 history edited YCor CC BY-SA 4.0
added missing definition
Oct 5, 2019 at 2:25 comment added Ami I use the definition $\operatorname{SO}_{2n}(k)=\{A\in\operatorname{GL}_{2n}(k)|A^TJ_{2n}A=J_{2n}\}$ where $J_{2n}$ is the identity matrix flipped 90 degrees
Oct 5, 2019 at 1:34 comment added LSpice Since your specific choice of $H$ (and the requirement that the upper-triangular matrices form a Borel subgroup) means that the form of $\operatorname{SO}_6$ matters, you should specify what form you use.
Oct 5, 2019 at 1:33 history edited LSpice CC BY-SA 4.0
Fixed some language (I think—preview looks strange)
Oct 4, 2019 at 23:25 comment added Misha You should look more closely at what's written and revise again: Since $G$ is supposed to have integer matrix entries, if the intersection is nonempty then $x=\pm 1, y=\pm 1$. Hence, $G\cap H=\emptyset$ for most congruence subgroups. I am not sure what happens for double cosets with Borel.
Oct 4, 2019 at 23:14 comment added Ami @Misha thank you, I edited my question a bit.
Oct 4, 2019 at 23:13 history edited Ami CC BY-SA 4.0
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Oct 4, 2019 at 22:59 history edited Ami CC BY-SA 4.0
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Oct 4, 2019 at 22:54 comment added Misha You can even take $G$ to be a "generic" Zariski dense 2-generated subgroup in $SO_6({\mathbb C})$. Then the intersection with $H$ will be empty. Here generic means that the two generators are chosen generically.
Oct 4, 2019 at 20:40 review First posts
Oct 4, 2019 at 22:16
Oct 4, 2019 at 20:36 history asked Ami CC BY-SA 4.0