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Dec
9 |
awarded | Critic |
Dec
7 |
answered | Never appeared forthcoming papers |
Nov
7 |
answered | What is the p-adic valuation of a number? |
Nov
4 |
comment |
What are the $p$-adic representations of $\hat{\mathbb{Z}}$ ?
@Kevin: yes I think so! Just to recap: the continuous image of a compact set is compact so the image has to land in a compact subgroup of $GL_n(Q_p)$ which we know is conjugate to a subgroup of $GL_n(Z_p)$. Conversely if $M = card(GL_n(F_p))$ and $f(1)$ is (say) in $GL_n(Z_p)$ then for every $k$, the image of $p^{k-1}M Z$ is in $1+p^k M_n(Z_p)$ so the map from $Z$ extends by uniform continuity. To relate this to Torsten's answer, it remains to check that a matrix is conjugate to an element of $GL_n(Z_p)$ iff its char poly has integral coeffts. |
Nov
1 |
awarded | Fanatic |
Oct
24 |
answered | Can an etale (phi, Gamma) module be an extension of non-etale ones? |
Oct
24 |
comment |
Can an etale (phi, Gamma) module be an extension of non-etale ones?
The last category is closed under extensions. What you mean is something different, isn't it? |
Oct
22 |
comment |
Citing papers that are in a language that you do not read.
I don't think it's necessary to have read the whole paper in order to cite it, but you need to point to a precise result in the reference, and explain the translation between the result as it's stated, and the results as you use it. I find it annoying when I see stg like "by [6], we have..." when [6] is a book, especially when the author of the paper is unable to say where in the book the result is when you ask him. |
Oct
11 |
comment |
When should a result be made into a paper?
@Kimball: Yes, Rota said that, see for instance: math.ohio-state.edu/~nevai/MYMATH/rota_ams_notices_01_97.html |
Oct
10 |
awarded | Good Answer |
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 |