bio  website  people.brandeis.edu/~jbellaic 

location  Stony Creek, ÉtatsUnis  
age  
visits  member for  4 years, 11 months 
seen  5 hours ago  
stats  profile views  15,014 
Professor of Mathematics at Brandeis University
17h

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Is there a nonabelian free group inside a group of positive rank gradient?
Thanks, Benjamin and Ycor, and Derek. Things are clear now. 
18h

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Is there a nonabelian free group inside a group of positive rank gradient?
I am still confused. What is a $p$group? For me it is a finite group of order a power of $p$. 
18h

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Is there a nonabelian free group inside a group of positive rank gradient?
I am not completely sure how to parse the statement of the theorem. Should "residually finite $p$group" be read together, meaning that the intersection of subgroups of index a power of $p$ is trivial ? 
2d

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Fell topology vs. convergence of matrix coefficients
Can you precise your definition of a primitive ideals? It is an ideal of what ring exactly? Thanks. 
Aug
22 
awarded  Nice Question 
Aug
22 
accepted  Applications of Lubotzky's linearity theorem? 
Aug
22 
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Applications of Lubotzky's linearity theorem?
Thank you Yves. I consider this as an answer  you may want to post it as such. 
Aug
21 
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Applications of Lubotzky's linearity theorem?
Comment meta: If several answers are proposed, I will add the tag "long list" and will request the post to be made CW. I have no objection if people make it CW right now anyway. 
Aug
21 
asked  Applications of Lubotzky's linearity theorem? 
Aug
13 
comment 
Inverse Galois problem for $GL_2$ of a compact local ring
Thanks for these interesting reflexions. My guess is that $\mathcal X$ is not countable but I don't see how to prove it. That should be an easy question for specialists of classifications of singularities. (BTW, I don't really believe in the conjecture that all universal deformation rings in our context should be complete intersection. That seems wishful thinking to me.) 
Aug
12 
revised 
Inverse Galois problem for $GL_2$ of a compact local ring
added 276 characters in body 
Aug
12 
comment 
Inverse Galois problem for $GL_2$ of a compact local ring
Thank Will. That answers the question as asked (initially). Unfortunately, the question I asked is not exactly the one I wanted to ask, which was "modulo the center". I tried to simplify it at the last minute when asking it and messed it up. I will change the question accordingly. 
Aug
12 
revised 
Inverse Galois problem for $GL_2$ of a compact local ring
added 34 characters in body; edited title 
Aug
12 
asked  Inverse Galois problem for $GL_2$ of a compact local ring 
Jul
30 
comment 
Fermat's proof for $x^3y^2=2$
I think we are too quick to say that Fermat had no proof of his claim about his equation. If you read Fermat's correspondance, you see there was a reason he rarely wrote down his proof: essentially no one would read them. When he talks to Pascal, for example, Pascal is eager to talk about probability, physics, and other subjects but show little appetite for reading Fermat's complicated numbertheory proofs. Fermat was simply too much in advance of his time. His best interlocutors would have been he Bernoulli and Euler, but they were born after his death. 
Jul
21 
revised 
A question on representation of graphs
edited tags 
Jun
11 
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Can every commutative ring of characteristic $p\in\mathbb P$ be written as the form $R/(p)$ with $R$ being a ring of characteristic $0$?
But then your second question needs precisions. It seemed to me it has been answered by Qiaochu's comment. But if you think otherwise, it is that I haven't understood the question as you intended it. Do you ask for which $S$ there exists a universal $R$? Anyway, I think you should throughly edit your question, removing the first question which has a trivial answer (or leaving it but indicating it has a trivial answer) and emphasizing the second one, formulated more carefully... 
Jun
11 
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Can every commutative ring of characteristic $p\in\mathbb P$ be written as the form $R/(p)$ with $R$ being a ring of characteristic $0$?
@Censi Li: Perhaps I have not said exactly what I meant: I meant a formulation of the question that makes it nontrivial. As it stands, it has the trivial answer $R=S \times \mathbb Z$ as proposed by LMB, and it is too easy a question for MO. If you can reformulate it in a way it has a nontrivial and useful answer, then I would be happy to vote to reopen it. 
Jun
11 
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Can every commutative ring of characteristic $p\in\mathbb P$ be written as the form $R/(p)$ with $R$ being a ring of characteristic $0$?
I have given the final vote to close, until the question is made more precise. 
May
26 
awarded  Popular Question 