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Jan 9, 2012 at 21:46 vote accept Maurizio Monge
Jan 9, 2012 at 17:59 history edited YCor CC BY-SA 3.0
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Jan 9, 2012 at 0:01 comment added YCor If $S$ is any nonabelian group $S^n$, the diagonal embedding of $S$ is not a normal subgroup! Hint: for $n=2$, compute $(g,1)(h,h)(g,1)^{-1}$... In a finite product $\prod_{i\in I}S_i$ of nonabelian simple groups, the only normal subgroups are the $\prod_{i\in J}S_i$ for $J$ ranging over subsets of $I$. It's an easy verification.
Jan 5, 2012 at 19:43 comment added Maurizio Monge I think that I'm missing something... in $S\wr{}G=S^{|G|}\rtimes{}G$, isn't the subgroup of $S^{|G|}$ formed by vectors with equal components a normal subgroup? In the case of $S$ elementary abelian the normal subgroups are exactly the sub-representations, why in the case that $S$ is non-abelian there should be no invariant subgroup? If $S$ is replaced by $S^{m_n}$, furthermore, all elements of $(S^{m_n})^{|G|}$ tuples with the first component equal (of the $m_n$) appears to be invariant under $G$.
Jan 5, 2012 at 0:01 history edited Alain Valette CC BY-SA 3.0
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Jan 4, 2012 at 23:55 history answered YCor CC BY-SA 3.0