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May 25th, 2017, 08:05 AM  #1 
Newbie Joined: Aug 2013 Posts: 16 Thanks: 0  Proving or disproving homomorphism from that map that maps (Z x Z) to S_3?
In mathematics, given two groups, (G, âˆ—) and (H, Â·), a group homomorphism from (G, âˆ—) to (H, Â·) is a function h : G â†’ H such that for all u and v in G it holds that h(u*v)=h(u)h(v). I have never done a mapping onto a permutation group though, so I am not sure how to approach this problem. Thank you in advance!

May 25th, 2017, 10:44 AM  #2 
Math Team Joined: Jan 2015 From: Alabama Posts: 2,647 Thanks: 680 
The function here maps the pair of integers (i, j) to the permutation . I presume that the operation on ZxZ is (i,j)*(m,n)= (i+m, j+ n). You want to show that, for any (i, j) and (m, n) in ZxZ, . Now, do you know what "(12)" and "(123)" mean here? 
May 26th, 2017, 08:57 AM  #3 
Member Joined: Jan 2016 From: Athens, OH Posts: 46 Thanks: 26 
Give the name $h$ to the mapping; i.e. $h(i,j)=(1,2)^i(1,2,3)^j$. The function h is not a homomorphism. First h is a surjective map: $h(1,0)=(1,2)$ $h(0,1)=(1,2,3)$ $h(2,0)=(1,2)^2=e\text{, the identity of }S_3$ $h(1,1)=(1,2)(1,2,3)=(2,3)$ (composition from right to left) $h(0,2)=(1,2,3)^2=(1,3,2)$ $h(1,2)=(1,2)(1,2,3)^2=(1,2)(1,3,2)=(1,3)$ The above equations show that every element of $S_3$ is an image. Fact: if h is a homomorphism from an abelian group G onto a group H, then H is abelian. You can try and prove this. So, if h were a homomorphism, then $S_3$ would be abelian, but it's not. Alternatively, if h were a homomorphism, $h(1,1)=h((1,0)+(0,1))=h(1,0)h(0,1)=(1,2)(1,2,3)$ $h(1,1)=h((0,1)+(1,0))=h(0,1)h(1,0)=(1,2,3)(1,2)$ But $(1,2)(1,2,3)\neq((1,2,3)(1,2)$ 

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disproving, homomorphism, map, maps, proving 
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