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12 votes
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A hyperbolic group with a small profinite completion

It's a famous open question whether every word-hyperbolic group is residually finite. Kapovich--Wise showed that this is equivalent to asking whether every non-trivial word-hyperbolic group has non-t …
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10 votes

Is there a residually finite non-elementary hyperbolic group whose profinite completion is b...

I'm fairly certain that no example is known. Of course, it's a famous open problem whether every hyperbolic group is residually finite. This turns out to be equivalent to many other questions about t …
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5 votes

An algebraic approach to the thermodynamic limit $N\rightarrow\infty$?

I doubt the following has anything to do with the thermodynamic limit. However, it has been pointed out that neither the inverse nor the projective limit of a sequence of $\mathbb{Z}/N$'s gives you $ …
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4 votes
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Bases of free groups

As Derek Holt says in comments, the answer to your first question is 'yes'. You can argue topologically. There is a rose $R$ corresponding to $X$ with $\pi_1R\cong F$. The subset $A$ defines a conn …
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3 votes

Are braid groups conjugacy separable?

(26 April 2016: Updated to give a fuller answer.) I'm fairly confident this question is still open. As Ian Agol points out in comments, the 3-strand braid group is, by a happy accident, also the fun …
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