4 votes
Accepted

Intuition for Luna's Étale Slice Theorem

Luna Étale's Slice Theorem is probably the most powerful result we have to understand the local structure of a moduli space. Moduli spaces (say of semi-stable vector bundles on a smooth projective ...
  • 6,533
3 votes

Structure of cuspidal Bernstein components—do non-commutative endomorphism rings ever really show up?

A lot of time has passed, so perhaps this question is moot for you [I mean, I saw you give the Plücker lectures last week on something very different], or perhaps you now know the answer. But since ...
1 vote

Schur multiplier of $\mathrm{SL}(2,\mathbb{Q})$

$\DeclareMathOperator\SL{SL}\DeclareMathOperator\Sp{Sp}$For a field $F$, the group $H_2(\SL_2(F))$ has a presentation in terms of the symplectic Steinberg symbols. This is shown in Matsumoto's paper [...
  • 329
1 vote
Accepted

A result of Borel on extensions of arithmetic groups

A proof appears in Section 2.3 of my paper Mapping class groups of manifolds with boundary are of finite type. As pointed out in the comments, it is crucial that $G$ is unipotent.
  • 7,658

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