985 reputation
617
bio website madore.org/~david
location Paris, France
age 37
visits member for 2 years, 11 months
seen 8 hours ago

2d
comment Flag manifolds (=R-spaces): quotients by parabolic subgroups vs. isotropy representation
I should add as a comment to this fairly old answer that the book Parabolic Geometries by Čap and Slovák, despite a slightly intimidating title, is excellent as an introduction to real and complex Lie groups and homogeneous spaces in general, and to answer my question in particular. (Arvanitoyeorgos's book is quite good, but only deals with the complex case of parabolic quotients.)
Jul
20
comment Can we define an “empirically generic” real number?
My initial formulation of the question was very unclear, I'm sorry about that, I hope I've made it better. No explicit real number can be generic, but we can hope for one to be "empirically generic-looking, in the same way that $e$ and $\pi$ are empirically random-looking (even though they are, of course, not at all random)".
Jul
19
comment Can we define an “empirically generic” real number?
I'm sorry my original formulation of the question was very messy and unclear. I tried reformulating it (starting from "edit/clarification") in a manner that I hope is clearer and less sweeping.
Jul
19
revised Can we define an “empirically generic” real number?
try to clarify the question and make it less informal by offering different formulation
Jul
18
asked Can we define an “empirically generic” real number?
Jul
10
revised Power series defined by Witt vectors / Teichmüller representatives of p-adics
Fix typo pointed out in comment
Jul
10
comment Power series defined by Witt vectors / Teichmüller representatives of p-adics
@Lubin: You're right. I replaced $\times$ by $\cdot$ everywhere.
Jul
10
revised Power series defined by Witt vectors / Teichmüller representatives of p-adics
replaced $\times$ by $\cdot$ for readability as per comment
Jul
10
revised Power series defined by Witt vectors / Teichmüller representatives of p-adics
added 573 characters in body
Jul
10
asked Power series defined by Witt vectors / Teichmüller representatives of p-adics
Jul
2
awarded  Curious
Jun
23
awarded  Necromancer
Jun
22
answered The difference between the Recursive and the Effective topos.
May
23
awarded  Nice Question
May
22
comment Real Lie groups versus real linear algebraic groups: differences in connexity and fundamental group
@YvesCornulier: Where can I find that statement (that the real points of a semisimple s.c. group are connected) written down and proven? That's exactly the sort of things I was wondering about, and what I was getting confused upon (e.g., the indefinite Spin groups: it doesn't help that no two authors can agree on how they are defined, let alone how connected they are); so this really explains a lot.
May
22
revised Real Lie groups versus real linear algebraic groups: differences in connexity and fundamental group
forgot to assume n is even (for there to be a difference between PGL, PSL and SL)
May
22
asked Real Lie groups versus real linear algebraic groups: differences in connexity and fundamental group
Apr
15
awarded  Popular Question
Apr
12
comment Non split extension isomorphic (as a group) to a split extension
I did some experimental testing with Gap, and (barring errors in my code) I've ruled out the existence of examples with the order of $E$ being, or, of course, dividing, one of: 128, 192, 288, 160, 240, 360, 400 or 336.
Apr
11
comment Non split extension isomorphic (as a group) to a split extension
@YvesCornulier: Where did Joseph prove this?