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Jul
14
reviewed Approve teaching tag wiki excerpt
Jul
8
reviewed Approve geometric-measure-theory tag wiki excerpt
Jun
23
reviewed Approve Why is differential Galois theory not widely used?
Jun
9
reviewed Approve rough-paths tag wiki excerpt
Jun
9
reviewed Approve rough-paths tag wiki
Jun
4
reviewed Approve Generalization of Krull dimension for commutative rings
May
29
reviewed Approve A question on an set of 8 matrices related to the SU(3) generators
May
29
answered Topologies on spaces of distributions and test functions
May
29
reviewed Approve Schubert Polynomials for Complex Projective Space
May
27
answered Searching for $C^*$
May
27
reviewed Approve How hard is it to make a differential operator Hermitian?
May
25
reviewed Approve How to understand a solenoid?
May
24
reviewed Approve Determinant of some covariance matrix (Gaussian kernel process)
May
22
reviewed Approve Is g( ) rational if it looks that way on a large rational subset?
May
21
awarded  Enlightened
May
21
awarded  Nice Answer
May
20
comment How bad can $\pi_1$ of a linear group orbit be?
I believe I understand how §5 and §6 show that $j^{−1}(L_vL′)$ and $j^{−1}(L_v\cap L′)$ are extensions: $$ 1→j^{−1}(L′)→j^{−1}(L_vL′)\xrightarrow{p∘j}A→1 $$ $$ 1→j^{−1}(j(M))→j^{−1}(L_v\cap L′)\xrightarrow{[\operatorname{mod}j(M)]∘j}F→1 $$ where $A=p(L_v)$ is (connected abelian Lie) × (free abelian of finite rank), and $F$ is finite. Embarrassingly I don't understand how §7 uses this to analyze $j^{−1}(L_v)$ and its $π_0$. Hopefully what I'm missing (perhaps some use of $1→L_v\cap L'→L_v→(L_vL')/L'→1?)$ was just "too obvious to bother mentioning".
May
19
revised Examples of TVS with no non-trivial open convex subsets
(statement was trivially false for finite-dimensional spaces)
May
19
answered Examples of TVS with no non-trivial open convex subsets
May
19
comment How bad can $\pi_1$ of a linear group orbit be?
Encore merci. Some (hopefully) nitpicking before I can begin to claim I understand your argument. Would you agree that: 1. In §1 of the proof, you need not really relax the hypothesis that $G$ is simply connected (for, modding out a connected subgroup does not change that)? 2. In §3, "$j(G)\subset H$" should be "$j(G)\subset L$"? 3. In §4, the very last $L$ should be $L_a$? 4. In §5, "virtually connected" should be "connected"? 5. In §6, the last sentence should be "so $\operatorname{Ker}(j)M$ has finite index in $j^{-1}(L'\cap H)$"?