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bio website perso.ens-lyon.fr/…
location Lyon, France
age 38
visits member for 4 years, 11 months
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I am a number theorist working in Lyon (France).

Oct
9
awarded  Commentator
Oct
9
comment Representation of vectors in $\mathbb{R}^2$ via differences of small vectors.
@André: yes indeed. Very nice. Problem solved!
Oct
6
comment Representation of vectors in $\mathbb{R}^2$ via differences of small vectors.
Indeed, Steinitz' theorem tells you about the radius of a disk centered at $0$ containing the partial sums, while fiktor's question is about the radius of a disk, possibly centered away from $0$, containing the partial sums.
Oct
5
comment Representation of vectors in $\mathbb{R}^2$ via differences of small vectors.
@Willie: Thank you for the reference!
Oct
5
answered Representation of vectors in $\mathbb{R}^2$ via differences of small vectors.
Sep
21
comment problems of subspace of M_n(C)
It's probably easier if the field is $\mathbb{C}$. For example take $k=n$ so the question is about subspaces such that any nonzero matrix is invertible. You see that any $2$-diml space of matrices contains noninvertible matrices (because if $A,B$ are two invertible matrices, then $\det(A+X \cdot B)$ has roots in $\mathbb{C}$). However, the corresponding problem over $\mathbb{R}$ is much harder, and is related to the maximal number of linearly independent vector fields on a sphere, which involves $K$-theory. See en.wikipedia.org/wiki/Vector_fields_on_spheres for details.
Aug
31
answered Numerical evidence of Beilinson's conjecture in local fields and function fields
Aug
25
awarded  Nice Answer
Aug
25
awarded  Editor
Aug
25
revised Refereeing a Paper
deleted 23 characters in body
Aug
25
answered Refereeing a Paper
Aug
23
awarded  Enthusiast
Aug
11
answered Power series $f$ such that $f(\zeta_{p^n}-1)=1/p^n$ for almost all $n \geq 0$
Jul
7
comment Subspaces of finite codimension in Banach spaces
Here's a fun exercise: take $E$ to be a Banach space and let $H$ be a codimension one subspace. Prove that $H$ is dense in $E$ if and only if $E \setminus H$ is arcwise connected.
Jul
5
answered Extension of valuation
Jun
23
awarded  Necromancer
Jun
11
comment Knuth's intuition that Goldbach might be unprovable
We do know that every even number is the sum of a prime and either a prime or a product of two primes. This makes the existence of a proof of Goldbach's conjecture sound rather plausible to me.
May
26
awarded  Enlightened
May
26
awarded  Nice Answer
May
25
comment Naive questions about “matrices” representing endomorphisms of Hilbert spaces.
It's chapter five in the 2nd edition, but there's still no counterexample...