# The only non-abelian simple group of order 60 is A_5

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• Nov 22nd 2011, 01:56 AM
alsn
The only non-abelian simple group of order 60 is A_5
Hi, assuming that a simple non-abelian group $\displaystyle$G$$of order 60 can be embedded in \displaystyle S_6$$, I want to prove that $\displaystyle$G$$cannot contain an odd permutation and is therefore a subgroup of \displaystyle A_6$$ (and then from that I can deduce that as it is order 60 it is $\displaystyle$A_5$$). How would I go about showing this? • Nov 22nd 2011, 06:49 AM Drexel28 Re: The only non-abelian simple group of order 60 is A_5 Quote: Originally Posted by alsn Hi, assuming that a simple non-abelian group \displaystyle G$$ of order 60 can be embedded in $\displaystyle$S_6$$, I want to prove that \displaystyle G$$ cannot contain an odd permutation and is therefore a subgroup of $\displaystyle$A_6$$(and then from that I can deduce that as it is order 60 it is \displaystyle A_5$$). How would I go about showing this?

Consider the sign map $\displaystyle \text{sgn}:G\to \mathbb{Z}_2$ where we're thinking of $\displaystyle G\hookrightarrow S_6$. Since $\displaystyle G$ is simple this is either zero or an embedding, and since $\displaystyle 60\nmid 2$ I'm pretty sure it's clear that the map is zero. But, this tells us precisely that every element of $\displaystyle G$ is even.
• Nov 22nd 2011, 07:10 AM
alsn
Re: The only non-abelian simple group of order 60 is A_5
Quote:

Originally Posted by Drexel28
Consider the sign map $\displaystyle \text{sgn}:G\to \mathbb{Z}_2$ where we're thinking of $\displaystyle G\hookrightarrow S_6$. Since $\displaystyle G$ is simple this is either zero or an embedding, and since $\displaystyle 60\nmid 2$ I'm pretty sure it's clear that the map is zero. But, this tells us precisely that every element of $\displaystyle G$ is even.

ahhh okay. so since all the elements of G map to zero and none map to 1, does this mean that all combinations of elements of G are even? think i get it.
• Nov 22nd 2011, 08:05 AM
Tinyboss
Re: The only non-abelian simple group of order 60 is A_5
Are you intending to make a distinction between "elements of G" and "combinations of elements of G"? The nature of a group is that combinations of elements are just elements themselves.
• Nov 22nd 2011, 08:13 AM
Drexel28
Re: The only non-abelian simple group of order 60 is A_5
Quote:

Originally Posted by alsn
ahhh okay. so since all the elements of G map to zero and none map to 1, does this mean that all combinations of elements of G are even? think i get it.

Like Tinyboss points out, this doesn't make sense per se. What I proved was that every element of $\displaystyle G$'s embedding in $\displaystyle S_6$ has even sign and so the embedding lives inside $\displaystyle A_6$.