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Jul 25, 2012 at 12:27 vote accept Joël
Jul 24, 2012 at 21:42 comment added Ian Agol This question has been considered by Troels Jorgensen: dx.doi.org/10.2307/2043555
Jul 24, 2012 at 19:33 history edited Andreas Thom
added group-theory tag
Jul 24, 2012 at 19:31 answer added Andreas Thom timeline score: 2
Jul 24, 2012 at 19:12 comment added Joël Done. Do you agree that $t$ is well-defined now ?
Jul 24, 2012 at 19:11 history edited Joël CC BY-SA 3.0
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Jul 24, 2012 at 18:24 answer added Bruce Westbury timeline score: 1
Jul 24, 2012 at 18:13 comment added Bruce Westbury Instead of adding comments, could you please edit the question?
Jul 24, 2012 at 17:57 comment added Joël For the existence, ind two matrices $a,b$ in $SL_2(\mathbb{C})$ such tr$(a)$,tr$(b)$ and tr$(ab)$ are algebraically independent (easy). Embed $\mathbb{Z}[X,Y,Z]$ into $\mathbb{C}$ by sending $X,Y,Z$ to these traces. Define $r: \rightarrow mathbb{Sl}_2(\mathbb{C})$ by sending $u$ on $a$ and $v$ and $b$. Then $t = tr \, r$ satisfies (1) and (2).
Jul 24, 2012 at 17:55 comment added Joël In this comment I sketch the proof of the existence and uniqueness of $t$. If $t: G \rightarrow K$ satisfies (2), that $t(gh)+t(gh^{-1})=t(g)t(h)$ for all $g,h$ in $G$, since this relation is satisfied for the trace of matrices in $\rm{SL}_2(K)$. With the "initial conditions" given in (1), one checks easily that $t$ is unique, and take values in $\mathbb{Z}[X,Y,Z]$.
Jul 24, 2012 at 16:40 history asked Joël CC BY-SA 3.0