Commutators and abelianisations of congruence subgroups in function fields











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Let $A = F_q[T]$ be the ring of polynomials in one variable with coefficients in a finite field, and let $r>1$ be an integer.
I'm currently looking for the abelianisation of the congruence subgroup $Γ(N)$ of the special linear group $SL(r,A)$, i.e. the kernel of the 'modulo $N$' map $SL(r,A) to SL(r,A/N)$, where $N in A$ is a nonconstant polynomial; more particularly, I'm looking for the torsion-free part of the abelianisation, but I wouldn't complain about knowing the abelianisation itself if that's possible.



So, here are my questions, in reverse order of importance:




  1. What are the commutator subgroups of $SL(r,A)$ and $Γ(N)$?

  2. What are the abelianisations of these groups?

  3. What are the torsion-free abelianisations of these groups?


I wasn't sure whether this should be posted on math.overflow instead; please move it if it should be there instead.










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  • 2




    Cross-posted to mathOF: mathoverflow.net/questions/315949/…
    – YCor
    Nov 22 at 11:58















up vote
1
down vote

favorite












Let $A = F_q[T]$ be the ring of polynomials in one variable with coefficients in a finite field, and let $r>1$ be an integer.
I'm currently looking for the abelianisation of the congruence subgroup $Γ(N)$ of the special linear group $SL(r,A)$, i.e. the kernel of the 'modulo $N$' map $SL(r,A) to SL(r,A/N)$, where $N in A$ is a nonconstant polynomial; more particularly, I'm looking for the torsion-free part of the abelianisation, but I wouldn't complain about knowing the abelianisation itself if that's possible.



So, here are my questions, in reverse order of importance:




  1. What are the commutator subgroups of $SL(r,A)$ and $Γ(N)$?

  2. What are the abelianisations of these groups?

  3. What are the torsion-free abelianisations of these groups?


I wasn't sure whether this should be posted on math.overflow instead; please move it if it should be there instead.










share|cite|improve this question


















  • 2




    Cross-posted to mathOF: mathoverflow.net/questions/315949/…
    – YCor
    Nov 22 at 11:58













up vote
1
down vote

favorite









up vote
1
down vote

favorite











Let $A = F_q[T]$ be the ring of polynomials in one variable with coefficients in a finite field, and let $r>1$ be an integer.
I'm currently looking for the abelianisation of the congruence subgroup $Γ(N)$ of the special linear group $SL(r,A)$, i.e. the kernel of the 'modulo $N$' map $SL(r,A) to SL(r,A/N)$, where $N in A$ is a nonconstant polynomial; more particularly, I'm looking for the torsion-free part of the abelianisation, but I wouldn't complain about knowing the abelianisation itself if that's possible.



So, here are my questions, in reverse order of importance:




  1. What are the commutator subgroups of $SL(r,A)$ and $Γ(N)$?

  2. What are the abelianisations of these groups?

  3. What are the torsion-free abelianisations of these groups?


I wasn't sure whether this should be posted on math.overflow instead; please move it if it should be there instead.










share|cite|improve this question













Let $A = F_q[T]$ be the ring of polynomials in one variable with coefficients in a finite field, and let $r>1$ be an integer.
I'm currently looking for the abelianisation of the congruence subgroup $Γ(N)$ of the special linear group $SL(r,A)$, i.e. the kernel of the 'modulo $N$' map $SL(r,A) to SL(r,A/N)$, where $N in A$ is a nonconstant polynomial; more particularly, I'm looking for the torsion-free part of the abelianisation, but I wouldn't complain about knowing the abelianisation itself if that's possible.



So, here are my questions, in reverse order of importance:




  1. What are the commutator subgroups of $SL(r,A)$ and $Γ(N)$?

  2. What are the abelianisations of these groups?

  3. What are the torsion-free abelianisations of these groups?


I wasn't sure whether this should be posted on math.overflow instead; please move it if it should be there instead.







group-theory abelian-groups function-fields






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asked Nov 20 at 13:54









Liam Baker

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  • 2




    Cross-posted to mathOF: mathoverflow.net/questions/315949/…
    – YCor
    Nov 22 at 11:58














  • 2




    Cross-posted to mathOF: mathoverflow.net/questions/315949/…
    – YCor
    Nov 22 at 11:58








2




2




Cross-posted to mathOF: mathoverflow.net/questions/315949/…
– YCor
Nov 22 at 11:58




Cross-posted to mathOF: mathoverflow.net/questions/315949/…
– YCor
Nov 22 at 11:58















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