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Nov 26, 2019 at 23:27 comment added YCor Unfortunately the question hasn't yet been solved (and doesn't seem out of reach) but an answer was accepted.
Nov 26, 2019 at 19:48 history edited darij grinberg CC BY-SA 4.0
edited body
May 30, 2015 at 13:10 vote accept Miel Sharf
May 29, 2015 at 20:48 history edited YCor CC BY-SA 3.0
for clarification, edited to remove the statement that Woess claimed the stronger statement
May 29, 2015 at 19:16 answer added Arturo Magidin timeline score: 4
May 29, 2015 at 10:00 history edited Miel Sharf CC BY-SA 3.0
added 12 characters in body
May 29, 2015 at 9:28 history edited Miel Sharf CC BY-SA 3.0
Making this a question instead of a reference request
May 29, 2015 at 8:59 vote accept Miel Sharf
May 29, 2015 at 9:23
May 29, 2015 at 8:44 review Close votes
May 29, 2015 at 12:27
May 29, 2015 at 8:25 comment added Derek Holt Ah well, I shall stop thinking about the original question now, but I would still be interested to know whether it is correct! I played with a few examples, and I could not find any easily described procedure for finding the torsion-free subgroup with the calimed properties.
May 29, 2015 at 8:22 answer added Alireza Abdollahi timeline score: 5
May 29, 2015 at 8:10 history edited Miel Sharf CC BY-SA 3.0
Clarification of my own stupidty
May 29, 2015 at 7:26 comment added Alireza Abdollahi @MielSharf: Could you please let us know on which page of Woess' article your claim is mentioned (or is used)? For upper central series is true. As every f.g. nilpotent group has a torsion-free nilpotent subgroup of finite index.
May 29, 2015 at 6:38 comment added Arturo Magidin @DaveWitteMorris: I'm not sure I follow what you are writing... are you reversing the roles of $N$ (original group) and $H$ (group we are looking for)? If we take the original group to be the integral Heisenberg group, then since $N/N_2\cong \mathbb{Z}^2$, $N_2/N_3\cong \mathbb{Z}$, and $N_3=\{e\}$, we can just take $H=N^1=N$. How did I get $H^2$ and $H^4$?
May 29, 2015 at 6:03 comment added Dave Witte Morris @ArturoMagidin: The solution requires more care than that. The OP's condition is satisfied for the integral Heisenberg group $H$. However, for $N = H^k$, the quotient $N/[N,N]$ contains the torsion subgroup $[H,H]^k/[H^k,H^k]$ of order $k$. Therefore, an example where your suggestion does not work is $H^2$. Your suggestion would replace this with $(H^2)^2 = H^4$, but that makes the situation worse, not better.
May 29, 2015 at 3:23 comment added Arturo Magidin Is there some reason that you cannot just take $N^k$, where $k$ is a common multiple of the exponents of the torsion subgroups of all $N_i/N_{i+1}$ ?
May 28, 2015 at 20:24 comment added YCor here's the MathSE link: math.stackexchange.com/questions/1301400/…
May 28, 2015 at 20:00 history edited Miel Sharf CC BY-SA 3.0
More accurate description
May 28, 2015 at 19:59 comment added Arturo Magidin Note that what you call "its central series" is usually called the lower central series.
May 28, 2015 at 19:24 comment added Miel Sharf I have asked this question in math.se, but failed to get an answer, which I do need urgently. Thanks for the help!
May 28, 2015 at 19:24 history asked Miel Sharf CC BY-SA 3.0