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6:29 AM
I'm just checking in to keep the room going :)
 
 
6 hours later…
12:13 PM
If $g \in F_2 = \langle a,b \rangle$ (free group on two generators) is such that $\langle g \rangle$ is normal, what can we say about $g$?
2
 
12:32 PM
Interesting. It turns out that $g$ must lie in the commutator subgroup $[F_2,F_2]$. The reason is that if it doesn't, then the abelianization of $g$ is nontrivial (the commutator subgroup is the kernel of the abelianization homomorphism). This can we used to show that the conjugacy class of $g$ is $\{g\}$. But this is absurd, because $F_2$ has the ICC property (infinite conjugacy class property).
Neat.
 
 
3 hours later…
3:52 PM
Thank you for sharing that, @user193319. It is neat :)
Does anyone know of an encyclopedia or miscellany of group presentations?
 

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